I think it's considered mixed or rapid cycling if you have extreme mood swings within the same day or week. To constitute either a depressed or manic episode it has to last a week or longer, sometimes can go on for months.

I'm mostly depressed, but I do have at times several hours or a whole day of hypomanic energy/enthusiasm, then swing back the other way. So those aren't truly "episodes", just a mood swing within the overall major depressive episode (going on for well over a year in my case).

Hope that helps.