90 was a number.
The Tenth Doctor recalled that he visited the Medusa Cascade when he was "just a kid" of 90 years old. (TV: Turn Left)
Halcyon was 90 light-years from Earth. (AUDIO: The Resurrection of Mars)
In the Twelve Galaxies, 90 forvalars were equal to 1 krin. (TV: The Ghost Monument)
The Time Scaphe's initial flight was intended to spend ninety minutes in the Time Vortex and return ninety days into the future. (PROSE: Cat's Cradle: Time's Crucible)