The show was maybe just about two hours. But we thought everything moved very quickly. When you are seated, the delicious pineapple bread and wonderful salad and fresh pineapple is already on the table. Then they take your drink order, and a little bit of entertainment takes place, including the part where the kids go up on stage to hula. Then that stops and they serve the main course. You eat and then dessert is served as the main show is starting.
I can understand your concern over going to the later show with little ones that age. That is the same reason we went to the early show. The later one would have been much too late for DD. We enjoyed it so much though, that I would say, if you go pretty regularly, maybe leave it till your next trip, if you might go at a cooler time of year, but if not, I would say go - heat or no heat.