I usually allow 1 hour from arriving at bus stop to being at restaurant. I figure buses are supposed to run at least every 20 minutes; then up to 20 minutes for the actual ride, then 20 minutes to get off bus, inside park, and to restaurant. Even if the restaurant is at a resort, I allow the same - you have to find your way thru a resort you may not be familiar with.
One time when we had a Wishes cruise, I wish I'd allowed a lot more - it took a lot longer to find and get to the boat dock at GF.
Also allow more time if you are using boats instead of buses.