Great atmosphere created for such simple graphics and a cool idea too! I see your observation about timing things with the music on a web build. I had a similar problem when I made Carol of the Bells (not a 3-hour game!). The way I solved it is to forget about delta time altogether. Instead, I used:
- The projectile's starting position
- The projectile's finishing position
- A timestamp of when the projectile started
- A timestamp of when the projectile was supposed to arrive at the destination
With these four variables I could calculate the position each frame by getting a ratio using Time.time in relation to the start/end time and then lerping that between the start/finish positions. Doing it this way means it doesn't matter how many FPS you're on, or what delta time works out to be, because you're recalculating based on the current time each frame.
Hope this helps!