I would think that you would have plenty of time. Just take the monorail on the 2nd floor of GF.
1) There is a sky bridge from the 4th floor of contemporary to the 5th floor of BLT. I usually DO NOT take this because I have found that sometimes it is only open to Magic Band access (for people staying at BLT), so I get off the monorail at the 4th (5th?) floor of Contemporary, go to 1st floor of contemporary on elevator or escalator, then walk outside to the ground floor entrance to BLT. There you can show your membership card and go on up. I hope someone will check me on this, because after this happened the first time, I did not try it again!
2) If you want drinks at TOTWL, get there in plenty of time to order, drink, and pay before 9PM. They will not let you run a tab and go outside on the roof deck before you pay. You can also order after the fireworks, if you are running late.
3) If you don't want alcohol because of being with your kids, they have ice water and cups in the TOTWL, so you can still enjoy it with your kids.
4) We went last two trips to watch the fireworks, and had a great time. Enjoy!