I would say it depends on the size of your party and what attraction you are trying to visit.
I was there solo last month and some days were really bad (really, really bad) weather wise, so I was changing parks, times and attractions on the fly. As a solo, I could even change 7DMT and A&E around with no issues. But the more people you are trying to get FP for, the harder it will be last minute. If you aren't trying for those two, it will be even easier.