Check out example codes for "unity timer with miliseconds". It will help you in understanding the concepts better.
Code Example 1
string FormatTime (float time){
int intTime = (int)time;
int minutes = intTime / 60;
int seconds = intTime % 60;
float fraction = time * 1000;
fraction = (fraction % 1000);
string timeText = String.Format ("{0:00}:{1:00}:{2:000}", minutes, seconds, fraction);
return timeText;
}
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