Could make it more accurate by using a moisture sensor and placing the prongs in the shower. Could also just add a smart button on the show door/wall that you press when you shower to reset the timer.
I have a water shutoff that I installed to cut my kids showers off, they have to press a button to turn on the shower valve. So it runs for 10min and then cuts off. Hmm my son forgets to shower often so maybe I should do something similar to remind him.