Most of your "studying" is the learning you do over the 3 years of residency (in clinic, by reading, and in prep for the ITE). You can't really "cram" that information in a few weeks in any sort of meaningful way. Though, all of us try to. Even though your attendings will constantly remind you about boards studying, and there's a weird social pressure / anxiety around boards in dermatology that is different from other specialties, you'll most likely be fine if you attended a good program with well-rounded training sites with a breadth of exposure to gen derm, med derm, peds derm, and derm surg.
Derm boards are HARD, but there's also a pretty high pass rate (97-98%). Literally ~10 people fail per year, and I suspect these are people at more questionable programs without good pathology or subspecialty exposure. I think the general consensus was that if you consistently scored above the 10th percentile on the ITE, you're golden. Between 5-10th, you should worry a little. Less than 5th, and you should definitely be worrying.