This was so much fun to play! I definitely think I spent the most time on your submission out of all the games I've rated thus far. It's such an inventive and clever mechanic that I could honestly see a full game made out of this with minimal changes. In fact, I sometimes forgot that I was even playing a jam submission at all!
I don't have too much of an issue with the paint disappearing quickly, and I really appreciate that the ammo is effectively infinite with a cooldown; I felt that it gave me a lot more freedom compared to if I had to pick up recharge packs or something. The only thing that I think is a genuine design issue is the fact that the "afterimage" of the player that the time travel mechanics works with is not included in the camera, which makes it hard to time certain actions when you get going really fast.
Overall though, that's a minor blemish on an otherwise awesome game. Amazing work!!