i do shut mine down 15 minutes after the light goes out and 30 minutes after light comes on, my vent turns back on.
for me, if i didnt shut down the fan with lights out. id lose 20ish *temp this time of year, and go from a on range of 78 to an off range of 58. also when my light comes on in the am, the room Warms up for 30 minutes (simulating the raising heat with raising sun) and then turns on to maintain a somewhat steady temp of about 78. dark time the room is about 65 at the low end with vent fan off. as humidity goes up, i ll run an in room fan for air cirulation, but my venting is for heat/cool control only. other fans will take care of simulated wind.