I think it ultimately stems from Star Trek VII: Generations. Kirk kept asking the captain of the new Enterprise when stuff would be installed (torpedoes, tractor beam, staff) and the answer for two was Tuesday, while the third Kirk said "let me guess. Tuesday?" Since I am not DanSteph I don't know if that's the ultimate origin of it with respect to the Orbiter community, but it would fit.
Martin Schweiger temporarily re-designated Monday as Tuesday
A useful tool... http://isittuesday.co.uk
And nobody questioned his authority to do so.