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Unable to parse DateTime with a custom format

After reading some other similar questions and trying their suggestions, I'm still unable to get my time to parse into a DateTime-
string time1 = File.ReadAllText(#"C:\Reminders\Reminder1Time.txt");
DateTime dt1 = DateTime.ParseExact(time1, "hh:mm:tt", CultureInfo.InvariantCulture);
dateTimePicker1.Value = dt1;
time1 is a string value of 9:00 AM Other questions have mentioned to use ParseExact to specify a custom format, but it's still not parsing.
The error I get thrown is on the second line
String was not recognized as a valid DateTime.
How would I get the dateTimePicker1 to display the value from the time1 string?

Looks like a stray colon and an extra h if you are expecting a 12 hour clock 1-12 without a leading zero and the AM PM marker with whitespace.
Try: h:mm tt
All of the formatting options are buried in the documentation, here.

var datefromFile = File.ReadAllText(FILELOCATION);
var format = "dd-MM-yyy hh:mm:ss,fff";
var formattedDateTime = DateTime.ParseExact(dateFromFile, format, CultureInfo.InvariantCulture);
Make your format Explicit, remember dd for date capital MM for month and yyyy for year. hh for hour mm for minutes and ss for seconds.
MSDN Formats:
https://msdn.microsoft.com/en-us/library/az4se3k1(v=vs.110).aspx

Convert String To Date

I want to convert dd/MM/yyyy to MM/dd/yyyy.
My code:
string g = "20-1-1999";
DateTime dt = DateTime.ParseExact(g, "dd/MM/yyyy", CultureInfo.InvariantCulture);
Error Message:
String was not recognized as a valid DateTime.

You have to give single M for month in format string. You can read more about format specifier MM, here and M here. You also need to using - as separator instead of /
DateTime.ParseExact(g, "dd-M-yyyy", CultureInfo.InvariantCulture);
If you expect day single digit you would give single d for day too.
DateTime.ParseExact(g, "d-M-yyyy", CultureInfo.InvariantCulture);
The "MM" Custom Format Specifier
The "MM" custom format specifier represents the month as a number from
01 through 12 (or from 1 through 13 for calendars that have 13
months). A single-digit month is formatted with a leading zero, MSDN
The "M" Custom Format Specifier
The "M" custom format specifier represents the month as a number from
1 through 12 (or from 1 through 13 for calendars that have 13 months).
A single-digit month is formatted without a leading zero, MSDN.

your format should be dd-M-yyyy
DateTime dt = DateTime.ParseExact(g, "dd-M-yyyy", CultureInfo.InvariantCulture);
var result = dt.ToString("MM/dd/yyyy");

Convert string to Time

I have a time that is 16:23:01. I tried using DateTime.ParseExact, but it's not working.
Here is my code:
string Time = "16:23:01";
DateTime date = DateTime.ParseExact(Time, "hh:mm:ss tt", System.Globalization.CultureInfo.CurrentCulture);
lblClock.Text = date.ToString();
I want it to show in the label as 04:23:01 PM.

"16:23:01" doesn't match the pattern of "hh:mm:ss tt" - it doesn't have an am/pm designator, and 16 clearly isn't in a 12-hour clock. You're specifying that format in the parsing part, so you need to match the format of the existing data. You want:
DateTime dateTime = DateTime.ParseExact(time, "HH:mm:ss",
CultureInfo.InvariantCulture);
(Note the invariant culture, not the current culture - assuming your input genuinely always uses colons.)
If you want to format it to hh:mm:ss tt, then you need to put that part in the ToString call:
lblClock.Text = date.ToString("hh:mm:ss tt", CultureInfo.CurrentCulture);
Or better yet (IMO) use "whatever the long time pattern is for the culture":
lblClock.Text = date.ToString("T", CultureInfo.CurrentCulture);
Also note that hh is unusual; typically you don't want to 0-left-pad the number for numbers less than 10.
(Also consider using my Noda Time API, which has a LocalTime type - a more appropriate match for just a "time of day".)

string Time = "16:23:01";
DateTime date = DateTime.Parse(Time, System.Globalization.CultureInfo.CurrentCulture);
string t = date.ToString("HH:mm:ss tt");

This gives you the needed results:
string time = "16:23:01";
var result = Convert.ToDateTime(time);
string test = result.ToString("hh:mm:ss tt", CultureInfo.CurrentCulture);
//This gives you "04:23:01 PM" string
You could also use CultureInfo.CreateSpecificCulture("en-US") as not all cultures will display AM/PM.

The accepted solution doesn't cover edge cases.
I found the way to do this with 4KB script. Handle your input and convert a data.
Examples:
00:00:00 -> 00:00:00
12:01 -> 12:01:00
12 -> 12:00:00
25 -> 00:00:00
12:60:60 -> 12:00:00
1dg46 -> 14:06
You got the idea...
Check it https://github.com/alekspetrov/time-input-js

how to convert 24-hour format TimeSpan to 12-hour format TimeSpan?

I have TimeSpan data represented as 24-hour format, such as 14:00:00, I wanna convert it to 12-hour format, 2:00 PM, I googled and found something related in stackoverflow and msdn, but didn't solve this problem, can anyone help me? Thanks in advance.
Update
Seems that it's possible to convert 24-hour format TimeSpan to String, but impossible to convert the string to 12-hour format TimeSpan :(
But I still got SO MANY good answers, thanks!

(Summing up my scattered comments in a single answer.)
First you need to understand that TimeSpan represents a time interval. This time interval is internally represented as a count of ticks an not the string 14:00:00 nor the string 2:00 PM. Only when you convert the TimeSpan to a string does it make sense to talk about the two different string representations. Switching from one representation to another does not alter or convert the tick count stored in the TimeSpan.
Writing time as 2:00 PM instead of 14:00:00 is about date/time formatting and culture. This is all handled by the DateTime class.
However, even though TimeSpan represents a time interval it is quite suitable for representing the time of day (DateTime.TimeOfDay returns a TimeSpan). So it is not unreasonable to use it for that purpose.
To perform the formatting described you need to either rely on the formatting logic of DateTime or simply create your own formatting code.
Using DateTime:
var dateTime = new DateTime(timeSpan.Ticks); // Date part is 01-01-0001
var formattedTime = dateTime.ToString("h:mm tt", CultureInfo.InvariantCulture);
The format specifiers using in ToString are documented on the Custom Date and Time Format Strings page on MSDN. It is important to specify a CultureInfo that uses the desired AM/PM designator. Otherwise the tt format specifier may be replaced by the empty string.
Using custom formatting:
var hours = timeSpan.Hours;
var minutes = timeSpan.Minutes;
var amPmDesignator = "AM";
if (hours == 0)
hours = 12;
else if (hours == 12)
amPmDesignator = "PM";
else if (hours > 12) {
hours -= 12;
amPmDesignator = "PM";
}
var formattedTime =
String.Format("{0}:{1:00} {2}", hours, minutes, amPmDesignator);
Admittedly this solution is quite a bit more complex than the first method.

TimeSpan represents a time interval not a time of day. The DateTime structure is more likely what you're looking for.

You need to convert the TimeSpan to a DateTime object first, then use whatever DateTime format you need:
var t = DateTime.Now.TimeOfDay;
Console.WriteLine(new DateTime(t.Ticks).ToString("hh:mm:ss tt"));
ToShortTimeString() would also work, but it's regional-settings dependent so it would not display correctly (or correctly, depending on how you see it) on non-US systems.

TimeSpan represents a time interval (a difference between times),
not a date or a time, so it makes little sense to define it in 24 or 12h format. I assume that you actually want a DateTime.
For example 2 PM of today:
TimeSpan ts = TimeSpan.FromHours(14);
DateTime dt = DateTime.Today.Add(ts);
Then you can format that date as you want:
String formatted = String.Format("{0:d/M/yyyy hh:mm:ss}", dt); // "12.4.1012 02:00:00" - german (de-DE)
http://msdn.microsoft.com/en-us/library/az4se3k1%28v=vs.100%29.aspx

Try This Code:
int timezone = 0;
This string gives 12-hours format
string time = DateTime.Now.AddHours(-timezone).ToString("hh:mm:ss tt");
This string gives 24-hours format
string time = DateTime.Now.AddHours(-timezone).ToString("HH:mm:ss tt");

Assuming you are staying in a 24 hour range, you can achieve what you want by subtracting the negative TimeSpan from Today's DateTime (or any date for that matter), then strip the date portion:
DateTime dt = DateTime.Today;
dt.Subtract(-TimeSpan.FromHours(14)).ToShortTimeString();
Yields:
2:00 PM

String formatted = yourDateTimeValue.ToString("hh:mm:ss tt");

It is very simple,
Let's suppose we have an object ts of TimesSpan :
TimeSpan ts = new TimeSpan();
and suppose it contains some value like 14:00:00
Now first convert this into a string and then in DateTime
as following:
TimeSpan ts = new TimeSpan(); // this is object of TimeSpan and Suppose it contains
// value 14:00:00
string tIme = ts.ToString(); // here we convert ts into String and Store in Temprary
// String variable.
DateTime TheTime = new DateTime(); // Creating the object of DateTime;
TheTime = Convert.ToDateTime(tIme); // now converting our temporary string into DateTime;
Console.WriteLine(TheTime.ToString(hh:mm:ss tt));
this will show the Result as: 02:00:00 PM

Normal Datetime can be converted in either 24 or 12 hours format.
For 24 hours format - MM/dd/yyyy HH:mm:ss tt
For 12 hours format - MM/dd/yyyy hh:mm:ss tt
There is a difference of captial and small H.
dateTimeValue.ToString(format, CultureInfo.InvariantCulture);

date problem in C#

if i have this in a string : 10/13/2010 8:38:40 AM
how to make it to this: 13/10/2010 08:38:40
thank's in advance

DateTime.ParseExact("10/13/2010 8:38:40 AM","MM/dd/yyyy h:mm:ss tt",CultureInfo.InvariantCulture).ToString("dd/MM/yyyy HH:mm:ss")
edited to make sure 24 hour clock is used in output

Use DateTime.Parse() to convert to a true DateTime object and then use the DateTime.ToString() method to output to the format you desire (code example coming):
var dateTime = DateTime.Parse("10/13/2010 8:38:40 AM");
var formattedString = dateTime.ToString("dd/MM/yyyy HH:mm:ss);

Quick and dirty:
DateTime.Parse("10/13/2010 8:38:40 AM", new CultureInfo("en-US")).ToString(new CultureInfo("en-GB"));
Since I know that those formats are for those cultures. However, you can read more about datetime formatting at:
http://msdn.microsoft.com/en-us/library/zdtaw1bw.aspx
Standard formatting:
http://msdn.microsoft.com/en-us/library/az4se3k1.aspx
Custom formatting:
http://msdn.microsoft.com/en-us/library/8kb3ddd4.aspx

Or for a more general solution, just pass a format string to DateTime.ToString('formatString'). For example, what you want is DateTime.ToString("dd/MM/yyyy HH:mm:ss"). This allows you to make any format you want.
Example:
DateTime exDT = DateTime.Now;
string exOut = exDT.toString("dd/MM/yyyy HH:mm:ss");
Here's a cheat sheet! You can use ":" where you want it
d Short Date
D Long Date
t Short Time
T Long Time
f Full date and time
F Full date and time (long)
g Default date and time
G Default date and time (long)
M Day / Month
r RFC1123 date
s Sortable date/time
u Universal time, local timezone
Y Month / Year
dd Day
ddd Short Day Name
dddd Full Day Name
hh 2 digit hour
HH 2 digit hour (24 hour)
mm 2 digit minute
MM Month
MMM Short Month name
MMMM Month name
ss seconds
tt AM/PM
yy 2 digit year
yyyy 4 digit year

var strfrom = "10/13/2010 8:38:40 AM";
DateTime dt = DateTime.Parse(strfrom, new CultureInfo("en-US"));
Console.WriteLine(dt.ToString(new CultureInfo("en-GB")));

var curDate = DateTime.Now.ToString() ;
string customDateFormat = Convert.ToDateTime(curDate).ToString("dd/MM/yyyy");

another variant, one one line:
DateTime.Parse("10/13/2010 8:38:40 AM", new CultureInfo("en-US")).ToString("dd/MM/yyyy HH:mm:ss");