It is too early to give another dose of revolution. One dose usually will take care of it but not always. The second dose would be given about a month after the first. Dry skin is very common in hedgehogs even without mites so if you see "dandruff" that is nothing to be really concerned about. If he is itching you can give him an oatmeal bath and that may help. If you have not cleaned and sanitized the whole enclosure, I would do that as well if you are concerned. That may speed up the process if there were some mites not on the hedgehog. If he does not have other symptoms, I would not worry. The whole process of losing quills was set in motion when he first got the mites and it does take a while for it to stop completely in some hedgies.
Here is the info on revolution https://animalhealth.pfizer.com/site...ept%202010.pdf