I think 90 minutes for a character meal is a good amount of time. I would also arrive at least 20 minutes early and check-in. Sometimes you are pleasantly surprised and seated well past your ADR time! (But character meals can cause delays) You could also ask for the check and pay early. Would you be heartbroken if you missed 1 character?
I have also read about/experienced a 15 minute grace period with the FP+ system. Now for something in high demand like FoP, I am unsure if the system would automatically do it or if it up to the discrection of the CM at the tapstile.
I would also not give up hope modifying the FoP FP+ or even the Tusker House breakfast! I know I am in
MDE moving things around today in anticipation for my FP+ window opening.