The 3 hours is more like a timer as the jam interpreted--with only development time counted(Obviously participants can still go overtime and log their time as overtime). Therefore, it is purely on the participators to pause and start the timer again and be honest with their time. In fact, the 3 hour timer isn't as big of a difference for me than 2 days, for I only get about 5-6 hours to allocate to my game creation in 2 days.
The time aspect of this jam is a fun challenge I try to keep up--sometimes I make a good game, sometimes--not so good. Most game in this jam are more of simple prototypes, just like an idea to test on for future development.
I think every Jam has to be different in some ways, and this is the way Trijam is interesting.