Disney have confirmed there would be fireworks in the time overlapping when Boo Bash guests can enter the park and day guests must leave. For August, that will probably mean the fireworks will go off at park closing at 9, before the 9:30 party starts. By the time the parties start at 9 (Sept/October), the fireworks may go off earlier or stay at park closing. Epcot, DCA, and other parks have often scheduled their fireworks at closing time.