Microspan

A microspan was a small unit of time. A precise definition was unknown, but it seemed to indicate a length of time somewhere between Earth seconds and minutes. Time Lords used the unit amongst themselves on Gallifrey (BFG: all of Gallifrey) — but the Doctor never attempted to make his companions learn about the unit.

A unit of the same name was also used by Terpsivores, but it was unclear whether a "Terpsivorian microspan" was the same thing as a "Gallifreyan microspan". Twelve Terpsivorian microspans were less than two minutes. (DWA: Death Disco)