I'm sure JW will come along and address any code issues. One possible concern I would have is potentially having two different breakers supplying the one box and exceeding the allowed number of conductors in the box. Powering a couple of relays and a timer may be a consideration.
A fan should be left to run for a length of time that may be longer than what the room is occupied. I have a HRV and use low voltage crank timers but of course they require manual activation.