I think the general timing would be to book a slot 1.5 hours before fireworks. Anything longer than that and you will probably be trying to drag it out. Like FSU Girl said, you can come back with your receipt and watch from the observation deck. Or keep watching for a later time slot or use the touring plans reservation finder to try to snag one closer to the that time frame. My husband and I had a 7:15 in May for a 9:00 fireworks and we had just finished up dessert when the fireworks started and we had eaten pretty slow. If you don't have a table by the window on the MK side, you may end up going out on to the observation deck anyway. There is also a room on the opposite side that overlooks the fireworks of the other parks. They wanted to put us in there last time when we had asked for a "fireworks view" but we asked to wait for MK side seating instead. Next time we will specify "MK fireworks view"