Sorry to say, but until Disney releases offical hours you may not know. I just checked for Sunday, July 6th, which is the end of the holiday weekend and there are no fireworks at MK that evening. There is a good chance on September 7th, a Sunday, there won't be any fireworks as it is the start of the slow season at Disney.
Hopefully things will change and you will be able to enjoy them on your anniversary but only time can tell. If not you could always plan a nice dinner at Epcot and watch Illuminations if your set on that night. Otherwise maybe look for doing the CG on the 6th.