It takes about a month for new skin cells to form. The topmost layer flakes off, and the new skin cells underneath slowly become the top layer, and then flake off. It would be crazy for anyone to think that there could possibly be dramatic results any sooner than a month in to a study.

How skin grows, dumbed down American Academy of Dermatology link: https://www.aad.org/public/kids/skin/the-layers-of-your-skin

They said that it was after 8 weeks that the medication started really working.
That totally makes sense -- it would take some time for the medication to stop the psoriastic process, so maybe a couple of weeks or a month before truly healthy, normal skin cells started forming. You can't expect a disease process that has been going on for years, to just disappear after one dose. It could easily take weeks or months for whatever the cause is to stop the cycle of damaged skin cells.

So if they started seeing results after 8 weeks, it seems like it takes about a month for much of the disease process to be halted. It seems logical that it could take longer, with higher doses, for some people.

8 weeks to start seeing clearance of a skin condition that has been present for years -- doesn't seem excessive to me.