8hrs on the river. Shuttle time 30-45min. Could easily make it 6hrs or 12hrs. Plus 10-20min dropping boat in and 10-20min at take out. More time at put in or take out if you are not dialed in and have never been there. I think the gate close at 7or 8 pm.
Gate closes at 8. If you don't make it back to the dam in time, like me last month, you have to walk down to your car. The gate will open from the inside when you drive your car up to it. With it getting dark earlier, shouldn't be a problem now.