Mania diagnostic criteria is that it lasts at least a week. Hypomania I believe can be a bit shorter. However, this can really vary from person to person. There is also rapid cycling, and ultra rapid and ultradian which is even faster, shifting within the day.

So really you should see a psychiatrist if you think you are bipolar. It could be bipolar, it could be something else. There are other mental illnesses that can look like bipolar, there are also many physical health illnesses that mimic bipolar quite well and some are serious. So it's important that you speak with your doctor about this. It isn't something you can self diagnose.