I ususlly make them 1-2 hours before wishes. It will depend on the time availadle. If, by chance, your dinner does not last 2 hours have your waiter refill your beverage and wait in the lounge. You can always order a drink at the bar and then go watch Wishes outside on the observation decks off of the restaurant!
We made our reservations about 1-1 1/2 hours before Wishes. If I remember correctly, our waiter said that if we finished dinner early, we could get a pass to come back up to the observation deck to watch the fireworks. You may want to check on that for sure.