Cobb County ordinance bans use of fireworks from 9 p.m. to 10 a.m., with several exceptions per Georgia law. The exceptions are January 1, the last Saturday and Sunday in May, July 3, July 4, the first Monday in September, and December 31 of each year. On these dates, consumer fireworks may be discharged until midnight, except on New Year's Eve, when they may be discharged after midnight until 1 a.m.

Cobb County Ordinances - Article VII. - NOISE
Sec. 50-257 - Enumeration of prohibited noises (15): Consumer fireworks. The use or exploding of consumer fireworks between the hours of 9:00 p.m. and 10:00 a.m., except on the dates, and at the times, explicitly specified in chapter 10 of title 25 of the O.C.G.A. (O.C.G.A. § 25-10-1 et seq.).

Georgia Law defines general rights and restrictions on where fireworks may be used, and who may use them. You may view this information by going to Georgia Code on LexisNexis and then within Title 25 - Fire Protection And Safety see Chapter 10  - Regulation of Fireworks.