Oh, I get the frustration, that's actually an animation bug. I messed up the formula for calculating the current frame, which causes the "fully grown" frame to appear one step before the plants actually finish growing.
As for the timer going into negative numbers, that's intentional! Since it's a Pomodoro timer, someone deep in focus might need a bit more than 25 minutes. To make sure that extra time doesn't eat into their break, it shows how much time has passed since the work session was supposed to end. Once you press the yellow button, the break begins and you can rest!
Thank you so much for the useful feedback!