If you were to stop today you'd probably have withdrawals that would be only slightly longer than had you just cold turkeyed the short acting opioids in the first place. I would say after two weeks you will be in the clear, and probably day 6 will be the hardest point of acute withdrawal, or the "hump". But it's really impossible to say, as everyone metabolizes drugs differently. For all we know the methadone can be running through you're system very fast at this point, in which case the withdrawals will be slower, if you have a slow metabolism, it will take longer.
But I'm kind of confused, did you say that you were able to stop the hydrocodone for a few weeks without problems?
When you got on methadone, we're you having to redoes multiple times a day to keep sickness away, or were you just psychologically addicted. If you didn't have real physical withdrawals when you switched to methadone, you can probably get off now with little to no withdrawals too. In fact if thats the case, and you didn't have a physical dependancy, you really should just get off the methadone immediately, because you will become addicted to that very soon.