Not sure if this does what you want, but I like using unix time stamp in
general:
double my_start_time, my_end_time, my_diff;
my_start_time = (DateTime.UtcNow - new
DateTime(1970,1,1,0,0,0)).TotalSeconds;
// for loop or some events goes in here
my_end_time = (DateTime.UtcNow - new DateTime(1970,1,1,0,0,0)).TotalSeconds;
my_diff = my_end_time-my_start_time;