Very interesting concept executed very well!
I felt the pressure of having to finish, and the constant ticking of the clock reinforced that perfectly! The client calling last minute is on the spot and made me chuckle the first time it happened.
I was a bit worried that I'd have to paint stuff precisely, but locking the paint mask to the area is a super creative idea to solve this! Also holding the right mouse button to reveal what should be painted was also very intuitive and nice to use!
My only gripe, is that the whole game is a bit too dark. Maybe there could be a light that flickers from time to time, would be nice.