A microspan was a small unit of time used on Gallifrey, (AUDIO: Weapon of Choice, et al.) shorter than a span (AUDIO: Forever) but longer than a nanospan. (AUDIO: The Inquiry) As employed by Lord President Romana, Darkel and K9 Marks I and II, it seemed to indicate a length of time somewhere between Earth seconds and minutes. (AUDIO: Gallifrey[which?]) Although Time Lords on Gallifrey used the term liberally, the Doctor never attempted to make their companions learn about the unit.
The materialisation of Romana's presidential TARDIS was once paused for two microspans. This lasted a little under one minute. (AUDIO: A Blind Eye)
A unit of the same name was also used by Terpsivores. Twelve Terpsivorian microspans were less than two minutes. (COMIC: Death Disco)
A Timonic Fusion Device could be armed for detonation in 45 microspans. (AUDIO: Weapon of Choice) Lord President Romana had a feature in her Presidential TARDIS which allowed for materialisation to be paused for two microspans. (AUDIO: A Blind Eye)