I have searched the Forum and have found a lot of information relative to using menthol to eliminate tracheal mites. Most information centers on whether or not to use menthol, how much to use, when to start using it, placement in the hive, etc. But I was not able to find the answer to one question if you have decided to use menthol for tracheal mites..................
When do you stop using it?
How many days should you leave it in the hive?
I know a beek who swears by a Halls' caugh drops stuck in back corner for both v.mites and tracheal mites.
I can't help answer your questions, since I only used it once and that was many years ago. The bees actually evacuated the hive for days. Tracheal mite resistant bees are the best answer.
(http://www.bushkillfarms.com/photos/d/897-1/DCP_0060.jpg)
I don't know very many people who use anything for tracheal mites anymore. They are really not much of a problem anymore. I've never used anything for them.
I'm sure you can find details on the MAARC site.
http://maarec.cas.psu.edu/pdfs/TRACHEAL.PDF