In the Star Trek universe, what would be happening on stardate 31415.9, the ultimage stardate pi day?
Something irrational, I bet.
They would celebrate with a cellular peptide pie. With mint frosting.
It’s green.
Well … since all the Stardates in ST:TNG started with 4, I’m guessing stardates that started with 3 would be from the decade before TNG.
Would that be the time of the NCC-1701-C Enterprise?
September 26, 2353 05:05:00 according to this site.
That matches pretty well with Memory Alpha’s timeline, as Seven’s parents left to follow the Borg in 2354 on Stardate 32611.2.
Given that, we can look at what they have for the year 2353. Notable things I see in that year are Jack Crusher’s (Wes’s Dad’s) death, Nog and Ziyal’s birth, and Kira’s mother’s death.
The Vulcans finally calculated the value of Pi to the last digit. 
Which caused their final break with the Romulans, who had arrived a different number.