I 100% agree with Weaver. People are different, and a level of time is not an accurate way to go. You don't want to end up in precipitated WD's. That's a scary place to be.
Google Cows chart to help you know when you are in moderate withdrawal. A length of time is not an accurate way to induce subs. I've seen people take them 24 hours after last methadone and not get sick and I've seen folks wait 48 hrs and get sicker than anything I have ever seen. When your arm hair stands up, eyes are displayed, sweats, and several other symptoms are listed on the COWS, I really in outage you look it up.