Does anyone know how much time is represented either as real time or game hours by the idle time box under partol data in an idlemarker? I'm not sure what number to put in to get about 30 min of game time.

I believe they are game hours, since they are meant to be used in conjunction with AI scheduled.

In-game time. It's safe to assume that anything that involves AI scheduling or behavior is based on in-game hours since the entire game revolves around routines/lives of actors in-game.