I asked my surgeon, he told me that it is mainly caused by the anesthesia. It can take weeks, depending on how long you have been put under. The longer you are put under, the more it will go into the system: after some time the anesthesia will enter the fat cells, where it will be stored and releases slowly after many weeks. In the worst case it can take 6 weeks. At the 6 week mark, one should feel a lot better.
Also, I ask my skin therapist today. She said it takes two years for wounds to be completely healed. After 1 year, things have settled, so any scar remediation has to be done in the 1 year mark, because after two years everything has settled permanently, including scars. She advised having scar therapy at the 6 month mark.