If parking is available at the other resort, (conventions may greatly limit free parking) 3 hours is customarily allowed for dining at the resort. (But not leaving the car at another resort to visit a park)
DVC points stays get free parking at WDW parks, too.
The only paid parking at WDW resorts is valet. (I think it's $20 or more + tip) since you pay for valet per day, there is no max length, even if you want to leave the car and visit a park.