You want the kids jumping and burning off energy while you actually get to drink a lukewarm coffee. Booking the earliest morning slot gets you a solid discount on the base package and a much quieter park before the afternoon crowds hit. Lock down the date four weeks out so you get the time slot you actually want.
A typical party runs about $600 once you add pizza, extra jump time, and good bags. That is a chunk of change to drop all at once, but you do not have to pay for the whole thing today if you map out the timeline carefully.
Remember that the intro window is a hard deadline, not free money. If you still have a balance left on the Discover it® Cash Back card when those 15 months are up, regular interest kicks in on what is left.