I am a worst-case scenario planner so I allow 1.5 hours from door to door from park to park or resort to resort. If I get there early I can look around, sit on a bench and relax, have a pre-meal drink, or maybe check in for my reservation (possibly being seated early).
I'm less worried if I'm going from resort to park and not trying to make it on time for a reservation/ fast pass.
I have a few cautionary tales but this is my favorite: We left BC 70 minutes before our Ohana reservation. Waited about 15 minutes for a bus to MK at BC. Arrived at MK, had to go through bag check to get to the monorail station. Got on the monorail with 20 minutes before our reservation. Monorail was held between the Contemporary and TTC. At the TTC we had maybe 5 minutes before our reservation, and didn't know if the monorail might be held again. DH got off the monorail and jogged to the Poly . . . only to be greeted with a line of 20 other people waiting to check in at Ohana (womp womp). Ultimately we were fine and the restaurants do typically give 15 minutes grace or so (they aren't required to!).
Bottom line, it would have been a MUCH more relaxing morning if we had just left earlier and allowed more time and DH could have probably enjoyed breakfast more had he not jogged over in the blazing heat.