This is my first year using thymol.
First started using cardboard strips soaked in the stuff, these were heavily chewed after 2 weeks and as mentioned in an earlier thread evaporated too fast I think as the bees definately did not like them for the first few days. Second treatment used oasis, the bees only nibbled at it a bit but in one of the hives after the 2 weeks the 2 pads were totally embalmed in propolis! So I dear say there remained some thymol left in them so I just flipped them over.
The drop was still high after 4 weeks treatment so I have put in another set of oasis soaked pads for the 3rd and final 2 week period of treatment.
Are you sure the bees have destroyed them? Has there been a significant drop of green debris on your tray, if not have they really gone or have they somehow got down between a couple of frames or worse blown out before you put the crown board on? If they have been chewed up by the bees then I'd put your 2nd treatment on. If one of the other 2 possibilities have occured then react accordingly.