I had been going back and forth last year a lot and when I finally got my script it felt like the subs were fake as they didn't do anything other than keep me from being sick.
As for how long to wait, I did become very sensitive to the induction based on how long I waited which is why I wait so long now. If I took it too soon (let's say @ 18hrs) then it would barely help, and wouldn't help that much at all for a few days no matter how much I took. But when I waited 36hrs I could actually feelit and it would work normally right away. So it came down to either taking it too soon and not having to suffer but not really feeling better for a few days, or suffering more for a few more hours and feeling positive effects from it right off the bat. I could tell a lot by how well the first dose worked.
What I always try to do is space out my usage to once every 24 hours so that my body adjusts to that so eventually I don't start getting too sick until 20-24 hours after my last use which makes waiting a little over 24 hours to start bupe much easier. After a while I didn't even start getting that sick until I was past the 24 hr mark which made it a lot easier to wait 30 hours or so, thus making the transition way easier.
Back in the day I would feel good from the bupe whenever, but it definitely lost it's magic the more I switched. Having said that, spacing out my usage and waiting longer as well as having a lower tolerance has made it easier to adjust again, but I feel it still has a lot to do with how long I wait. Most people are using more dope more often the longer they go though, so me doing the opposite isn't the norm.
I had always been skeptical of posts saying that bupe lost it's magic the more times you switched until it happened to me. There are definitely more variables at play though other than just the number of times you have switched. So as bad as this may sound, if you are on bupe or use it in between runs then plan your relapses better if you can.