One thing to keep in mind is that if there's inclement weather, the parade may be cancelled. You can then change your FP+ to something else, but by that time of day, there's not likely to be much available. We had that happen to us last Tuesday. It was raining on and off that afternoon, and they cancelled the parade at the last minute, while we were in line to enter the FP+ area. We tried to change our FP+, but there was very little available, so we wound up just leaving and going back to the resort for a while. Then we couldn't get another FP+ for the parade during our stay, so we wound up watching it from Frontierland on a different day.