You mean recreationally? I'd normally recommend 10mg and work from there. Effects from the Oxy and H should be reduced and on the way out by the time it kicks in, but of course that depends on how much you've done and how doped you are, so give them more time before dosing the methadone if needed until effects are substantially reduced. See how 10mg affects you, giving it at least 3 hours or so to take full effect before even considering a redose. It's creepy shit, so be cautious with it.
It's long half life means there'll still be some activity tomorrow, its effects being cumulative with daily dosing over a coupla days or so, so half of what you take today maybe enough to get you to around the same place, same dose again possibly being too much. Would not advise you go anywhere near 30mg or above. First time I did it at 30mg with little opiate tolerance I was borderline dangerous dose and puking for two days. Treat with caution.
