The way I am reading your request is, you are wanting to control the fans from either bath with manual timers that wind up and unwind ?..
The first problem I see is that say, the master bath timer still has time running on it. Someone is in the guest bath and sets their timer. The run time of the fan is going to be controlled by whichever timer is set for the longest time. The guest may not want the fan on, but it will stay on until the master bath's timer runs down to shut it off or vice versa. (Are we both thoroughly confused now ?)