> "as soon as possible after the software launches"

This isn't true, just desired, and is one of the main roots of the conflict here. OF COURSE you would like to start selling in advance and then have billing start with customers the instant the "last" pr is merged. That isn't a realistic view of the software world though and pretending it is while everyone knows otherwise starts to feel like bad faith. Making software that works, then having time to deploy it, make changes from early feedback, and fix bugs is important. THEN all the other business functions should start the cant-take-back parts of their work that need to coordinate with the rest of the world. Trying to squeeze some extra days from the schedule is a business bet you can make but it would be nice if the people taking this risk were the ones who had to crunch or stay up all night or answer the page.

Trying to force complicated and creative work into a fake box just so you can make a gantt chart slightly narrower only works on people a couple times before they start to resent it. 10x that if management punishes someone when that fantasy gantt chart isn't accurate and 100x that if the one punished is the person who said "it's impossible to know" and then was forced into pretending to know instead of the person doing the forcing.