How long does bipolar mania last?

If untreated, Manic episodes can last a few days to weeks.
Depends on patient. A few days or a few hours, and even within a few minutes in some cases. This is what is known as rapid-cycling.
Variable. Manic episodes generally last a few days, but can last longer. Untreated episodes can lead to hallucinations and delusions especially if not sleeping. The impulsivity can lead to relationship, financial, or even legal problems.