I had already made my FP + reservations before the MK opening time changed to 8 am. Is it reasonable to plan on riding Buzz Light Year, Tea Cups, Winnie the Pooh and Little Mermaid before my 9:15 FP for SDMT?
Yes. Your 9:15 SDMT FP works till 10:15, so if the first three attractions take longer(I don’t think they will) then an hour fifteen, you can still use your FP.
Make a personalized TP (including the FPPs you already have) and Optimize it to find the best things to do at RD.
We had nearly the same happen to us mid-April and it was wonderful! We were able to do Space, Buzz x2, JC, PoC, and HM before arriving at SDMT around 9:45 for our 9:00 FP. I agree with making a personalized TP - ours was highly accurate.