H.F.
Honestly, for my kids, it always seemed to vary according to the activity they were doing. If it was something they really really wanted to do, they might do it for 45 minutes or more. But most activities, it seemed to be about 20-30 minutes (if they weren't against doing it). If it is something they don't want to do, they might not even give it 2 minutes. Mine are now 8, 3 and 5 months.
Good luck. I hope this helps.