Count Running Time by valve trigger

Hello,

I have a process where a valve is opened and dumps material into a holding thank, and theres usually about a 1 hr lag before my pumps begin to run and empty out the holding tank.. I'm trying to write a calculation to calculate the hours that this described process ran.

I.E the opening of the valve triggers the timer then the closing off of the pump would end the timer. Theres two PItags for both teh valve and the running of the pump

Any help would be much appreciated!

Thanks