Fireworks games for the 2017 season are scheduled for July 3, July 4 (also against the Reds) and Friday, September 29 (against the Los Angeles Dodgers). All three games are scheduled to begin at 6:10 p.m. (Mountain time).
Tickets for these games are always in high demand (and also come with a higher price). However, if you’re still looking for seats to the games, here is the link to the official ticketing site for the Rockies and fireworks games.
The fireworks display usually starts 20-25 minutes after the final out of the game has been recorded.