How long does it take for scabies to go away after permethrin cream?

Depends. Even if all the scabies mites are killed by the premethrin, itching can persist for several weeks. Persistent itching, especially if there are big bumps, sort of like mosquito bites, can be treated with a topical cortisone (steroid) cream. Usually premethrin is applied twice, about a week between applications. It has to be done right, clothes and bedding washed, contacts treated too.