System.DateTime truncate Milliseconds

There are many ways to achieve this, but first you need to do

 System.DateTime.Now - startTime

ins$$anonymous$$d

 startTime - System.DateTime.Now

But you can easily solve your problem by doing this

 TimeSpan elapsedTime = DateTime.Now - startTime;
 text.text = string.Format("Time : {0:D2}:{1:D2}:{2:D2}", elapsedTime.Hours, elapsedTime.$$anonymous$$inutes, elapsedTime.Seconds);