How long does mania last at the shortest amount of time?

Mania: The best answer I can give you, is that it depends on the patient. In bipolar disorder, for some, there is a phenomenon known as rapid cycling. This means moods can be extremely labile, switching from extreme highs to extreme lows in variable lengths of time from a couple of hours, on down to a few minutes.

ZeroCertainty, mania: like other "diagnostic" terms=only a label for a pattern; does not reflect accuracy or great understanding of the pattern for which the label is used/applied. This is particularly true for diagnoses of mental behavior patterns: complex, individually unique & typically lacking detailed relevant understanding by others; answers=within. Mania&Depression=both evasion behaviors for underlying issues.