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Convert total time into minutes in C#

I am developing a C#(WinForm) application with the goal of recording the service time of a task, and would like the help of you to solve this case.
I need to register two different times, in two different variables (Both have to be current computer schedules), because I will have a start and end time. So I need to calculate this time between the schedules and turn the result into minutes and display it in a TextBox.
I also need to have a total value in minutes and convert this value to time in "hours: minutes".
The code I have is the one below. If anyone can help me, thank you!
private void GetHoras()
{
DateTime total = DateTime.Now;
string totalTime;
totalTime = total.ToShortTimeString();
txtTempo.Text = totalTime;
}

What you're looking for is the TimeSpan struct.
If you subtract one DateTime from another, you'll get a TimeSpan result automatically.
It has members that can give you total minutes or seconds or hours, etc., or the individual parts.

You can use Substract function:
DateTime date1 = DateTime.Now.AddHours(-2).AddMinutes(-25);
DateTime date2 = DateTime.Now;
TimeSpan interval = date2.Subtract(date1);
int hoursDiff = interval.Hours;
int minutesDiff = interval.Minutes;
double minutesTotal = interval.TotalMinutes;

double totalMins = dateTime1.Subtract(dateTime2).TotalMinutes
Works for Me with a double value of total minutes as result.

Get undertime and overtime automatically

Could you please help me? I'm trying to create an attendance system wherein the undertime and overtime will be automatically computed, but there's an error. For example the employee's scheduled out is 11 PM, and their overtime 12 AM which is 1 hour, but the output is 23. Can anyone help me how to compute elapsed time?
string datetime = "12:00 AM"; // this is the time you are going to time out
string OUT = "11:00 PM"; // this is your scheduled out
DateTime d1 = Convert.ToDateTime(datetime);
DateTime d2 = Convert.ToDateTime(OUT);
TimeSpan ts = d2.Subtract(d1);
MessageBox.Show(ts.TotalHours.ToString()); // output is 23 which is wrong, it must be 1 hour overtime only

IMO, in order to fix your problem, you have to work with the actual datetime objects.
Always record actual system datetime without manipulating parts of it.
For your case you should have the fields for record scheduled_work_start, scheduled_work_finished and actual_work_finished
for an instance, say one of the employees starts work at 10-01-2019 14:00:00 (2 PM) and finishes her time at 10-01-2019 23:00:00 (11 PM) and assume she did one hour overtime.
The system should record the actual_work_finished time as 11-01-2019 00:00:00 (12 AM)
When you require to calculate or find out the extra time
calculate:
var over_time_in_hours =
actual_work_finished.Substract(scheduled_work_finished).TotalHours;
Hope this makes sense.

If you print your d1 and d2 times:
d1 time => "09.01.2019 00:00:00".
d2 time => "09.01.2019 23:00:00".
Then 23-0 = 23 is the expected result.
By the way you can achieve your result by adding 1 day to d1 time object and subtract this result from d2 object:
TimeSpan ts = d1.AddDays(1).Subtract(d2);
Console.WriteLine(ts.TotalHours.ToString());

Let's start by naming your variables something that helps us to reason about the code.
// this is the time you are going to time out
DateTime actual = Convert.ToDateTime("12:00 AM");
// this is your scheduled out
DateTime scheduled = Convert.ToDateTime("11:00 PM");
TimeSpan overtime = scheduled.Subtract(actual);
What we find is that you're performing the wrong calculation to start with. This would be the correct calculation:
TimeSpan overtime = actual.Subtract(scheduled);
When we do that though we are now getting -23 hours. This is because your actual time isn't after your scheduled time. For that you need to add a day.
Try this:
// this is the time you are going to time out
DateTime actual = Convert.ToDateTime("12:00 AM").AddDays(1);
// this is your scheduled out
DateTime scheduled = Convert.ToDateTime("11:00 PM");
TimeSpan overtime = actual.Subtract(scheduled);
Then you get the result that you want - i.e. 1 hour.

C# TimeSpan calculating hours

I am trying to create a time card solution in C# and having an issue with totaling hours worked for a week. From a drop down, the user would select the number of hours they worked in a day (ex. 5:30 - the 5:30 is the total hours worked, not the actual time 5:30). The user would select the hours each work day and the application would then total the hours for the week. The application I have written totals the hours, but I have two issues: if I use .Hours to add the hours up, I run into an issue when the total goes over 24; when I use .TotalHours, it calculates over 24 ok, but somehow it adds an hour randomly when I select :30 increments. Here is the code I have to calculate and display the totals:
using .Hours does not allow the total number of hours to go over 24. Instead it converts the 24 to 1 day and starts the adding the hours again, losing the original 24:
lblWorkgroupOneTotalTime.Text = (totalWeekOneHours.Hours).ToString("00") +
":" + (totalWeekOneHours.Minutes).ToString("00");
//using .TotalHours causes the calculation to randomly add an hour to the total:
lblWorkgroupTwoTotalTime.Text =
(totalWeekTwoHours.TotalHours).ToString("00").TrimStart('0') +
":" + (totalWeekTwoHours.Minutes).ToString("00");
I feel like I am very close to having everything work correctly, but I can't figure this part out.

How about this:
Initialize an example for 30 hours and 30 minutes:
TimeSpan totalWeekThreeHours = new TimeSpan(30, 30, 0);
(Timespan works better than DateTime here I feel.)
Then:
var hours = (int)totalWeekThreeHours.TotalMinutes / 60;
var mins = totalWeekThreeHours.TotalMinutes % 60;
Output:
var example1 = hours + ":" + mins;
var example2 = String.Format("{0} hours {1} mins", hours, mins);
Console.WriteLine("Example 1: " + example1);
Console.WriteLine("Example 2: " + example2);
//Output:
//Example 1: 30:30
//Example2: 30 hours 30 minutes

it adds an hour randomly
Nothing in programming happens "randomly". So when debugging, your first step should always be to look for patterns in your bug. As long as you believe the bug happens "randomly", you will have a mental block getting in the way of finding the bug.
As for your specific issue…
For any of the Total... properties of TimeSpan, this will be a double value that represents the entire time span in the units you're retrieving, including any fractional amounts.
For example, if the TimeSpan value represents 1 hour and 45 minutes, the TotalHours value will be 1.75. At the same time, you are telling the ToString() method that you want the value rounded to the nearest integer value. So, any time that the fractional part of your time span in hours is greater than one-half, the value is rounded up to the next hour value.
If you don't want that behavior, you should just truncate the value yourself before formatting it as a string:
lblWorkgroupTwoTotalTime.Text = string.Format("{0:0}:{1:00}",
(int)totalWeekTwoHours.TotalHours, totalWeekTwoHours.Minutes);
I also don't see why you used the format string "00" only to strip off the leading 0 after the fact. Easier to just not format the string that way in the first place.
Finally, note alternative syntax for formatting strings. Your approach (calling ToString() explicitly) is fine, but I find it wordy. The above is more concise, and does a better job separating the format from the input values.

The problem with displaying TotalHours with a format string of "00" is that it's going to round up. You have a couple of choices if you don't want to show days:
Use Hours + Days * 24 for the hours
Use TotalMinutes / 60 for hours
Convert TotalHours to an int, which will always round down
For example:
var totalHours = (totalWeekOneHours.Days * 24) + totalWeekOneHours.Hours;
// Or:
var totalHours = totalWeekOneHours.TotalMinutes / 60;
// Or:
var totalHours = (int)totalWeekOneHours.TotalHours;
Then you can output it:
lblWorkgroupOneTotalTime.Text = $"{totalHours:00}:{totalWeekOneHours.Minutes:00}";

Datetime UTC/GMT time to local time "where I am"

Let's say that I have this DateTime(Mar/01/2015 09:55:52)
I want to know if that time (I think this time is from Germany, anyways, I'm living in Brazil and the difference between us is 4hours).
So basically:
DateTime I have: Mar/01/2015 09:55:52
DateTime.Now That representes "where I am": Mar/01/2015 05:55:52
I want to make this parse to tell me, for example, if that "DateTime that I have" is 1 minutes after at least and 10 minuts later at maximum from the "DateTime where I am".

If you are on .net 4.5 - you can use the TimeZoneInfo class, it has a ConvertTime method that lets you pass in a datetime and a timezone
TimeZoneInfo.ConvertTime Method (DateTime, TimeZoneInfo)
you can use it like:
DateTime dateTimeIhave = TimeZoneInfo.ConvertTime(dateTheyGave, theirTimeZone, yourTimeZone);
if (dateTimeIhave > DateTime.Now.AddMinutes(1)
&& dateTimeIhave < DateTime.Now.AddMinutes(10))
{
doSomething();
}

//pseudocode
//DateTime that represents where you're at = dnow;
//DateTime that you have = dhave;
//convert dnow and dhave to seconds using this algorithm:
//convert the time into a string and get the data using a parser.
//int seconds = current seconds;
//seconds += minutes * 60;
//seconds += hours * 60 * 60;
Then find out if both times are between 60 seconds and 600 seconds from each other.

Time Math Guidance needed

I have a DateTime object that is 10:00 AM
This time represents what time of day a report should be run.
I want to calculate the amount of time remaining from NOW until 10:00 AM
part of my confusion is NOW might be after 10:am or BEFORE 10am,
I keep playing around with TimeSpan, but my results are not quite right... I am sure this is simple, but it is one of those things I have been working of for a few hours and I need a push in the right direction...
I want the timespan object timeTillRun to be correct...here is what I have tried:
{
DateTime scheduledRun = DateTime.Today.AddHours(_timeToStart);//_timeToStart = 10
TimeSpan timeTillRun = DateTime.Now - scheduledRun;
}

This will work... but you need to reverse the order of subtraction:
TimeSpan timeTillRun = scheduledRun - DateTime.Now;
Note that if it's currently after 10AM, timeTillRun will be negative. You will presumably also need to check if the current time is on or after 10AM, then add 10 hours and one day to DateTime.Today to obtain the next run time. Alternatively, you could test if timeTillRun is negative; if so, just add one day to it (timeTillRun += new TimeSpan(1, 0, 0, 0)).

Try this
DateTime timeToStart = DateTime.Today.AddHours(10);
TimeSpan timeTillRun;
// Checking to see if current time is passed schedule run, if it is then we add a day (this is assuming this is run daily, if days are skipped like weekends for example then this would need some tweaking)
if (DateTime.Now > timeToStart)
timeTillRun = DateTime.Now.AddDays(1.0) - timeToStart;
else
timeTillRun = DateTime.Today - timeToStart;
double totalHoursRemaining = timeTillRun.TotalHours; // get total hours remaining
string prettyRemaining = String.Format("{0} day and {1} hours", timeTillRun.Days, timeTillRun.Hours); // can do some outputting here