I think you have time to watch and wait as long as your airline is cooperative. We had Saturday arrival time but I finally just canceled through Monday today. I waited until last minute. If on Monday, it looks like northern FL got hit really bad (or along I95, which is what we have to take) then we will cancel the remaining part of the trip.
As for lower crowds, I thought that too but others have posted that lots of people go to the parks afterward b/c school will be out and many can't get back in their homes. I thought that was strange. Not sure I could go to a park not knowing if my possessions are still there, but I suppose to keep the kids busy