I dug quite deep into this and apart from occasional reports of actual gate guards saying 3 hours, since actual parking tickets were replaced by Magicband scans I can find no evidence for a specific time any more.
The Disney T&Cs just say you can park at resorts as follows.
Complimentary standard self-parking is available while enjoying select dining, shopping, entertainment, and recreation experiences at Disney Resort hotels.
Having said that OP, any of the Monorail resorts are especially tight on entry, Contemporary is the hardest to get into apparently.
The somewhat secret trick if you just want to avoid hassle is to ‘bump and run’ a dining reservation. I’ve done this for the day we’re touring the monorail resorts just to make life simple. Booked a table for 1 at The Wave, will get waved in to park because I have an ADR, and then you can modify then cancel the ADR as long as it’s more than 20 minutes before your reservation. You can’t directly cancel it btw, you have to modify it more than 24 hours in the future, THEN cancel.
Thanks to the Backside of Magic podcast for that idea.