Average time is about 90 minutes. Though it can vary greatly one way or the other. There are no set routes for the buses, so you have no way of knowing ahead of time if you will be the first stop or the last. And you have no way of knowing ahead of time how quickly you will get on the bus, and how quickly that bus will depart.
In any case, you should leave at least 3 hours from your scheduled flight arrival time until you have your ADR. That gives enough time to get to your resort, get checked in, and get to your meal. Barring any flight delays. If a meal is really important and you would be crushed to miss it, it isn't a good idea to book it on arrival day. Too many things can happen to cause you to be late and miss it.
Oh, I see you want to eat at your resort. That should shave at least 30 minutes off. But I wouldn't cut it too close.