Originally Posted by
Narcissa
Technically ultradian bipolar has been described, but it's not especially common, and I imagine that more often than not the differential diagnosis is BPD.
So you're correct, episodes can last less than a day, but it's the exception to the rule really.
Rapid cycling is actually defined by the frequency of the manic and depressive episodes, not their duration, and I believe in the case of rapid cycling bipolar the standard criteria for the duration of episodes typically holds.