For me, it took about 6 months before everything settled down. I had it from the get-go; my cancer was right on the anus muscle. So, 6 months of sitting awkwardly - usually, I'd slightly perch on one cheek and switch to the other when that became sore. I was perched on the sofa with my legs folded up, lying a bit against the arm. I tried a few different bum supports, inflatable rings, etc. The best one was a medical standard square thing that came in a big box with its own pump, provided for free by the local health nurse. Typical H&S nonsense, it couldn't be given back when I no longer needed it! I think it's packed away somewhere, against the day when I get hemorrhoids!
There was a bit of, um, moisture - mucus? from the wound for most of that time. No biggie, just shower more often, and wear the thinnest women's pantie pads, located a bit further to the rear than where they were intended for. Darn, those things are cheap! €0.02 each or something. But they don't stick awfully well to (men's) underwear, or maybe I was doing it wrong - at least I worked out that they are not meant to stick to the skin - at my age who could I go ask about it? The shop assistant - LOL? Maybe I should have searched out the ones with wings?
Due to Covid, etc., I haven't had a chance to ask my surgeon about one aspect of the Barbie Butt. Maybe it's just me, but sometimes it feels like the area (perineum, I guess) gets inflated, or bulges down a bit. I can't see it, and I have nobody to ask, and I'd feel a bit of a pervert doing upshots! But there is noticeable wear on the crotch of underwear - I'm buying underwear much more often these days. On the other hand, I have been doing much more walking, and recently cycling, than I did pre-BB.
Finally, for a while, there is an element of phantom-bum. Your stomach is telling you to go sit on the loo, your brain is telling you there's no point. And something inside you says how satisfying a good long...evacuation...would be.