what i found about this format up until you branch into singles, gets REALLY bad towards the middle, cuz people who are closer to the end, have to leave. so my suggestion would be ALL group shots first, THEN singles for ALL the groups. because a lot of people don't have time to do single shots, ESPECIALLY when there is only one hour per group and others might have other shoots or events to go to! i lost a LOT of people at the KH photoshoots at Sakuracon as well as last years' Kumoricon, i would advice you to do all groups first, then singles, just so you won't lose people.