Sum time field

Is it possible to script for cumulative total of a time field?

I am using the following script to fetch time from one form to another:

for each PeopleRecord in People[ID in input.People_lookup]

{

//fetch participation record

ParticipationRecord = Participation[ID in PeopleRecord.Participation_dates];

//update record

PeopleRecord.No_hours_participated=Time_spent;

}

This only gives me the most recent 'time' from the record. Is there a way of doing a cumulative total time?

Thanks!