Very cool concept! i can easily see this being built into something bigger. It's also crazy that you made all this in 20 hours. On my (Chrome, Windows) setup i did have some issues with the timing of the shoot sfx helper/indicator. As it got out of sync from the main track after about 30 sec.
I see you're using Godot! woop woop! If you want to continue building this project. I recommend looking into the BPM feature for .ogg files or the AudioStreamSynchronized. Maybe these features could help with that potential issue. Or maybe it was just me that was bad at timing my shots. Thanks for the game - Keep it up :)