Why isn't my TimeSpan.Add() working?

Question

There has to be an easy answer:

var totalTime = TimeSpan.Zero;

foreach (var timesheet in timeSheets)
{
   //assume "time" is a correct, positive TimeSpan
   var time = timesheet.EndTime - timesheet.StartTime;
   totalTime.Add(time);
}

There's only one value in the list timeSheets and it is a positive TimeSpan (verified on local inspection).

Answer 1

TimeSpans are value types. Try:

totalTime = totalTime.Add(time)

Answer 2

This is a common mistake. TimeSpan.Add returns a new instance of TimeSpan.

Answer 3

totalTime = totalTime.Add(time)