I just made FP+ reservations for days listed as 5/6/7. I actually forgot so didn't make them until about 7 am Eastern. (In the past, I've tried to do them as soon as the window opened at midnight or 1 am). Had no trouble at all. Surprised to see that even Anna & Elsa was available - but I'm not interested in that one, anyway. IMO, you'll be just fine to do them first thing in the morning.