How to have the time counting system activated?

In the game,I am trying to create, there is a need to count and display the number of passed hours between two events. Please,help me! Thanks!

Hi,
Thanks for the response,
In a more complicated situation, the promised time (the first event) is,let us say, March12,2010 at 17:52 and actually something was done on this matter on November 7,2012 at 05:22(the second event). I do not know how let Excel to know that it is to count the number of hours (if needed,minutes,seconds etc) have passed between the two events.
All my gratitudes,

OK, so you already have two times in two cells and you need to know the number of elapsed hours, minutes, seconds (not days).

If the earlier time is in A2 and the later time is in B2, use this formula:

=TEXT(B2-A2,"h:mm:ss")

Thanks a lot,Jazzer!
I'll try now!