Hi Paula,
I'm a big fan of Characters in Flight! If the timing works out just right, you may be able to catch a glimpse of the fireworks at the Magic Kingdom or Epcot. However, reservations are not accepted so there is no way to guarantee that your flight will be timed just right to be able see to see the fireworks. The flight including ascending & descending lasts approximately 10 minutes so it could be time to come down just as the fireworks are starting. I have been on when there was no one else waiting in line so we got to stay up a couple of minutes longer. However, this is a popular attraction & I don't think that happens very often.
Weather conditions govern whether or not they can fly. Wind conditions play a big part in how many people are allowed in the gondola at one time & how high they can ascend. If the conditions are perfect, 29 guests plus the pilot can ascend up to 400 ft.
The night & day flights are two different experiences. Depending on visibility you are able to see a greater distance during the day. The lights during the nighttime flight are beautiful. Be sure to take your binoculars & camera. The pilot will walk around and take pictures of you and your party once you've reached the maximum height for your flight.
The lines can get pretty long depending on what time of day & season you visit. If you decide to do a daytime flight, I suggest that you arrive a few minutes before opening. Hours of operation are 9 a.m. - 12 midnight (weather permitting) 7 days a week. Tickets are purchased near the loading zone near Planet Hollywood at Downtown Disney's West Side.
I highly recommend Characters in Flight. It may not be something you'll do every visit, but its something everyone (except those super afraid of heights) should experience at least once. Wishing you many magical memories :-) Allison