Be pretty hard to implement anyway unless you were balancing it for very low level player parties. 90 days is barely any time at all when players can spend twice as much time grinding up money for supplies and/or babies for Kiyoko's emergence scene.
Eh, you can pretty easily smash through the entire MSQ in like 1-2 months.
But yeah I hate time-based mechanics like that; the only "oops you failed" I'll likely do is act-based gating -- like with LivreaQuest needing to be done in Act 1.