I have never been on methadone maintenance but am currently on sub maintenance. And from what I have seen and heard from friends of mine who switched from 'done to sub is that some of them took the sub way too early after being on relatively high doses of methadone for years and went through pure hell after doing that. Some of them waited a little longer to switch from done to sub and ended up being fine. Everybody is different and has different metabolisms. I myself can do any full agonist opioid(excluding methadone, only tried it a couple times when I was dope sick and had nothing else) and take sub like 8-10 hrs after and be fine because I have a super fast metabolism, If I were you I would wait at least 3-4 days making the switch or possibly take some super weak opioids in between the switch just to keep you from getting too sick, like Vicodin or Percocet, then jump on the sub after 24 hrs of withdrawls from them. I have heard that's the easiest way to switch. I know a lot of people who have made that switch and everyone had different ways of doing it. good luck!