I'm with Midwest Mom on this. ODD doesn't start at age 8. I know that there are teenagers that will all of a sudden exhibit those symptoms, but there were always signs. My daughter has had her "issues" her whole life. As soon as she could talk and move, those things came out. ODD was the first label they gave her because she was too young to be able to tell more. Now we know a ton more of what's going on, and we know there is still stuff that is yet to be nailed down, that will come out during or after puberty.
The fact that he'd sit in a time out before this, I'd say it's not ODD, but a reaction to something in his environment. Social, family, food, etc.