Cars and coffee begins at 7:30 but the cruise part is scheduled for 9:45.
If you made it by 8:30 or so you should be fine. There is parking for 500 cars....don't think it will be full an hour after it starts.
If your asking when a bunch of motorheads partying on Saturday night will end...... I would say very late.
I am not sure if GM has anything specific planned for Saturday yet. Has that info been released.