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C# How to convert UTC date time to Mexico date time

see my code which i used to convert Mexico date and time to UTC date and time.
string strDateTime = "25/01/2017 07:31:00 AM";
DateTime localDateTime = DateTime.Parse(strDateTime);
DateTime univDateTime = localDateTime.ToUniversalTime();
ToUniversalTime return UTC 25-01-2017 02:01:00
when again i try to convert the same UTC date and time UTC 25-01-2017 02:01:00 to Mexico local time then i got 24-01-2017 06:01:00
so see 07:31:00 AM becomes 06:01:00 which is not right. so tell me what is missing in my code for which i am getting wrong local time when i convert from utc to Mexico time using timezone info.
see my code which converting from utc to Mexico local time using timezone info.
string strDateTime = "25-01-2017 02:01:00";
DateTime utcDateTime = DateTime.Parse(strDateTime);
string nzTimeZoneKey = "Pacific Standard Time (Mexico)";
TimeZoneInfo nzTimeZone = TimeZoneInfo.FindSystemTimeZoneById(nzTimeZoneKey);
DateTime nzDateTime = TimeZoneInfo.ConvertTimeFromUtc(utcDateTime, nzTimeZone);

You current time zone (UTC+05:30) is different from the time zone you are converting into (UTC-8:00). So you get the difference. There is about 13 hours and 30 minutes difference from your original time zone to the targeted one. 5:30 - (-8) = 13:30.
Subtract 13 hours and 30 minutes from your original date, and then you get 18:01:00, which in 12-hour format is 6PM on the previous day.
Edit:
Instead of hard-coding Mexico time zone, you will need to have a method by which you can determine user's time zone no matter where they are coming from. This is best done using JavaScript as outlined in this answer.

Okay, I didn't know that you were located in India - which changes things a little bit:
You're going to want to utilize the TimeZoneInfo.ConvertTime() API for this one.. Maybe something like :
var dt = new DateTime(2017, 01, 25, 7, 31, 0).ToUniversalTime();
var nzTimeZone = TimeZoneInfo.FindSystemTimeZoneById("Pacific Standard Time (Mexico)");
//var ist = TimeZoneInfo.FindSystemTimeZoneById("India Standard Time");
DateTime nzDateTime = TimeZoneInfo.ConvertTime(dt, TimeZoneInfo.Utc, nzTimeZone);

Your problem is that the Parse is done without specifying the timezone it comes from - therefore the system will use whatever the default is of your computer. It appears that Your computer is NOT in PST. Rather somewhere in India.
Therefore after turning it into a DateTime object you need to convert it to UTC by specifying the PST timezone. There are a few ways to do this:
Specify the timezone offset as part of the string.
Call one of the TimeZoneInfo.ConvertTimeToUtc and specify the timezoneid
Maybe all you want to do is convert between two timezones by calling ConvertTime or ConvertTimeByTimeZoneId.
https://msdn.microsoft.com/en-us/library/bb382770(v=vs.110).aspx
https://msdn.microsoft.com/en-us/library/bb382058(v=vs.110).aspx
string pst = "Pacific Standard Time";
TimeZoneInfo.ConvertTimeBySystemTimeZoneId(currentTime, TimeZoneInfo.Local.Id, pst));
For example: 7:30AM PST should be 1:30 UTC - not 2:30. So that suggests a problem in the initial conversion. 2 AM UTC to PST is indeed 6 PM. Also I noticed your input was 7:31 and you claim it output 2:01 -- does Mexico do 30 minute timezones? I know India does.
I use Google to test conversions by literally searching for "2:01 UTC to PST" and it returns the answer for comparison.
See this other post which shows declaring the input timezone for Parsing. And as stated one does NOT need to convert for DST. Does ConvertTimeFromUtc() and ToUniversalTime() handle DST?
More info on MSDN for TimeZoneInfo: https://msdn.microsoft.com/en-us/library/bb495915(v=vs.110).aspx

Different time output for ToUniversalTime

I cannot understand or find any information that could explain why there are two different time component output (12p.m and 11 a.m) for the following. Can somebody please explain.
DateTime d1 = new DateTime(2015, 05, 15).ToUniversalTime();
DateTime d2 = new DateTime(2015, 02, 02).ToUniversalTime();
Console.WriteLine(d1.ToString()); //OUTPUTS - 1/05/2015 12:00:00 p.m.
Console.WriteLine(d2.ToString()); //OUTPUTS - 1/02/2015 11:00:00 a.m.

The ToUniveralTime method converts from the local time zone where the code is running, to UTC.
Since time zones can change their offsets from UTC at different times of the year, the value can easily be different between two different dates - especially since one date is in the winter, and the other is in the summer, due to daylight saving time.
See also, the DST tag wiki, and "time zone != offset" in the timezone tag wiki.

Julian Time stamp to Date Time

I am trying to convert to Julian Time Stamp to Date Time. I have the following microseconds time stamp 212302469304212709. As i understand i need to add these milliseconds to the beginning of Julian Calendar (January 1, 4713 B.C., 12:00 (noon)). So i have the following method:
private DateTime GetDateTime(string julianTimeStamp)
{
var julianMilliseconds = Convert.ToDouble(julianTimeStamp)/1000;
var beginningOfTimes = new DateTime(1, 1, 1, 0, 0, 0, 0);
var dateTime = beginningOfTimes.AddMilliseconds(julianMilliseconds).AddYears(-4713).AddMonths(-1).AddDays(-1).AddHours(-12);
return dateTime;
}
Assume i pass 212302469304212709 string as the parameter. The expected result should be 2015/07(July)/01 00:08:24.212. Based on my method, i have almost the same result, but day is not 1, it is 6. Same problem for different time stamps i tested.
Could any one tell me what i am doing wrong? Thanks in advance.
Edited:
This is the exact date time i expect to receive: 2015(year) 7(month) 1(day) 0(hour) 8(minute) 24(second) 212(millisecond) 709(microsecond)

The given timestamp 212,302,469,304,212,709 μs when converted to days (just divide by 86,400,000,000) gives 2457204.505836 days (to six decimal places, which is the best I can do without a lot of extra trouble). Using the Multi Year Computer Interactive Almanac (MICA) written by the United States Naval Observatory, and putting in the free form date 2015(year) 7(month) 1(day) 0(hour) 8(minute) 24(second) 212(millisecond) 709(microsecond), the program calculates exactly the same day count (to six decimal places), proving the time stamp is an accurate Julian date.
One problem with the OP's calculation is trying to use the DateTime class before the earliest supported date, as pointed out by another poster. Also, the OP didn't say if 1 July 2015 was in the Julian or Gregorian calendar, but the MICA calculation proves it is in the Gregorian calendar. Since the OP is working in the Gregorian calendar, the epoch of Julian dates should be stated in the Gregorian proleptic calendar: Noon Universal Time, November 24, 4714 BC. The oft-quoted date January 1, 4713 BC is a proleptic Julian calendar date.
"Proleptic" means a date has been found by beginning at a modern date, who's calendar date is known with absolute certainty, and applying the rules of the chosen calendar backward until the desired date is reached, even though the desired date is before the chosen calendar was invented.

DateTime uses Gregorian calendar, so when you substract years, months and so on you are doing it with that calendar, not the Julian.
Unfortunately DateTime does not support dates before year 1. You can check the library in this post, maybe it helps you.

Is there a way to instantiate a datetime object in a timezone other than local?

I've been racking my brain all afternoon trying to figure this one out. Essentially, the problem itself seems simple. I'm given a date/time that is representative of a date and time in another time zone (not local). I want to convert this value to a UTC value to store in the database. However, all of the methods I find online seem to point to you either starting with UTC or starting with a local time zone. You can convert TO other time zones from these, but you can't start with anything other than those. As a result, it appears that I'll have to do some kind of convoluted offset math to do what I want. Here is an example of the problem:
var dateString = "8/20/2014 6:00:00 AM";
DateTime date1 = DateTime.Parse(dateString,
System.Globalization.CultureInfo.InvariantCulture);
var currentTimeZone = TimeZoneInfo.FindSystemTimeZoneById("Pacific Standard Time");
// Now the server is set to Central Standard Time, so any automated offset calculation that it runs will come from that point of view:
var utcDate = date1.ToUniversalTime; // This is wrong
// Similarly, if I try to reverse-calculate it, it doesn't work either
var convertedDate = TimeZoneInfo.ConvertTime(date1, currentTimeZone);
utcDate = convertedDate.ToUniversalTime; // This is also wrong
In essence, I want to somehow tell the system that the datetime object I'm currently working with is from that time zone other than local, so that I know the conversion will be correct. I know that I'll eventually need to figure Daylight Savings Time in there, but that is a problem for another day.

Would this method be of any use to you ?
The TimeZoneInfo.ConvertTime method converts a time from one time zone
to another.
Alternatively, you could use the ConvertTimeToUtc method to simply convert any date (specifying the source time zone) to UTC.
var dateString = "8/20/2014 6:00:00 AM";
DateTime date1 = DateTime.Parse(dateString,
System.Globalization.CultureInfo.InvariantCulture);
var currentTimeZone = TimeZoneInfo.FindSystemTimeZoneById("Pacific Standard Time");
var utcDate = TimeZoneInfo.ConvertTimeToUtc(date1, currentTimeZone);

The System.DateTime struct only has two bits for storing the "kind" information. That is why you can only have "local" or "universal" or "unknown" (or "magicl local").
Take a look at the System.DateTimeOffset struct. It is like a DateTime, but it also keeps the time zone (offset from (plus or minus) UTC).

DateTime.Today , beginning or end of the day?

I am using DateTime.Today.
Now I'm not sure if the date is from the beginning of the day or the end of the day.
This is what DateTime.Today returns : {11-3-2014 0:00:00}

MSDN states the following: "An object that is set to today's date, with the time component set to 00:00:00."
This means that a DateTime object is created with today's date at the absolute start of the day hence 00:00:00.
You can check if it is the start of the day by using the AddHour() method of the DateTime class.
DateTime d = DateTime.Today;
//AddHours, AddMinutes or AddSeconds
d = d.AddHours(1);
if (d.Date != DateTime.Today.Date)
{
//Not the same day
}
If d.date should be different the date was initialised at a different time (eg. 23:00:01).
http://msdn.microsoft.com/en-us/library/system.datetime.today(v=vs.110).aspx

0:00:00 is the start of the day and 23:59:59 is the end of day.
You can also confirm through this 24-hour clock
In the 24-hour time notation, the day begins at midnight, 00:00, and the last minute of the day begins at 23:59. Where convenient, the
notation 24:00 may also be used to refer to midnight at the end of a
given date[5] – that is, 24:00 of one day is the same time as 00:00 of
the following day.
On a side note:-
If you want to know the time then use .Now because that includes the 10:32:32 or whatever time; however .Today is the date-part only (at 00:00:00 on that day ie the begining of the day). So you can say that .Today is essentially the same as .Now.Date

Thats the beginning of the day, the end of the day would be:
{11-3-2014 23:59:59}
And remember, the only stupid question is the one you don't ask :)

DateTime.Today returns the current DateTime value, without the Time part.
Which means, it is the the first possible DateTime value for the current day.

Think of it like this:
The last moment in a day can be 23:59 or theoretically any amount of nanseconds before the next day. the next day then starts at 00:00:00 counting upwards.
So 11-3-2014 0:00:00 marks the beginning of a day. Either the earliest possible moment, or no time at all, if you want to treat 0:00:00 as a default value.