I think you are setting your trip up to be stressful right out of the gate. You never know if your flight will be delayed, if you need to take extra time during check-in, how long it will take to not only get to the park, but do you really want to shoo the kids straight to the attraction after waiting so long to get into the park?
We never even schedule a park on arrival day. If we go, we go. If we don't and explore, that is how we do it. I have had to rush for an ADR, and it was not fun. No way would I begin a trip worrying about a FP time.