If I take 5mg of methadone a day in the morning. Is waiting 10hrs long enough to able to take my. 5mg of ativan (lorazepam) and be safe?

Possibly not. If you have been taking methadone for quite a while at that dose or same with Ativan, (lorazepam) you may be tolerant. When these two classes of medications are taken together , especially for the first time , they may have a multiplicative sedating effect. The Methadone has a long half life so it would still be in your blood. You should have all of your medications coordinated by one physician.