It would be difficult to squeeze in a lot of the places rkkwan mentioned if you're commited to Tai O, as it's quite a ways away and I'd imagine you'd be feeling pretty tired by mid-day (I know I would!).
Wong Tai Sin Temple would be possible though, as it isn't too far from where you're planning to be at night on Monday. Not sure about hours of operation though, might be closed by 5:30pm.