Welcome to Bluelight!
This is the perfect place to ask such a question but you will never get a good answer without some additional information. Have you used opiates or been addicted? How much methadone are you taking and how long is the course you will be taking it (one 40mg dose vs 3 40mg doses for 1 each day for 3 days)
Generally one can hope to get 12-72 hours of being not dope sick from methadone but it depends on a lot of factors. If you take one small dose you are likely to get 12 hours if the dose was "too small" for your tolerance. Where as I had been on methadone maintenance for 3 months at 90mg a day and when we had a major snow storm wanted to see how long before I got sick, it was about 60ish hours before I took my methadone and even then I could have gone longer.
Let us know more about your dose and we can help!