For temple tours, I really recommend that you do this on your first day since it would take one whole day of exploring. Thailand have a lot temples and all very beautiful. I also recommend that you dress modestly, no mini-skirts, shorts and sleeveless clothes. Most of the temples are open 8 am to 4 pm and beware of swindlers. We encountered those people at the entrance of the Grand Palace, a man approached us acting all official and told us to proceed to the next entrance since the entrance we were at was for the locals. So we followed and proceeded to the entrance that he mentioned, but when we got to the other entrance there was another man who approached us and said that we could should not go in the Grand Palace now because there are having a worship ceremony and that we should visit other temples first and come back around 3 pm. Conveniently they have a friend who's a tuk-tuk driver that would take us around the other temples near the area for a fee of course. We ignored them and decided to go back to the first entrance we went and follow the flow of the tourist and lo and behold there was no worship ceremony at all. In the Grand Palace the workers wore uniforms so I suggest you only talk to them rather than some stranger.
This picture of the building looks like it was mirrored which made it really cool.