....the reason the access time isn't reliable is that is can be overwritten by applications outside of the actual user....
You read but failed to fully understand. All someone has to do is plug the drive in on a system that has not had access times disabled and open a directory. Since virtually all PC's have an anti-virus suite installed this will result in the AV scanner scanning all the files in that directory, which triggers an update to the "Last Accessed Date". This makes that field useless as an indicator that any of the files were actually viewed. You only know that the stick was plugged into another computer, not that anything else occurred.
If you really want to protect your files you should be encrypting your drives.