Assuming the timer on the fan has been set to something sensible like 15 minutes, the fan should only run for a short time after the light has been switched off.
You have indicated that you think the light is left on all night.
The question has to be, why is this person leaving the bathroom light on all night??
Most fan set-ups like this have what is known as a 3 pole fan isolator - which should isolate just the fan completely. This should be situated in a convenient place.
If there is one, perhaps your neighbour could kindly switch it off before each long session every night of leaving the bathroom light on.