Before I started with my current company, there was a legislative deadline that gave an agency 30 days to implement some pretty substantial changes, roughly 60 days of full-time work for the entire team. Apparently the folks writing the bill felt that 60 days was too long and the agency should just figure out how to do it.

This also happened to be during a hiring freeze, so no new contractors, no temp employees, nothing. Current team of half a dozen or so had to drop everything they were doing, switch over to this project and work ~12 hour days six days a week just to deliver a mostly-broken implementation right at the deadline and spend another week and a half at the same schedule fixing bugs and other issues.

It would have been much worse if the timelines were extended, if it was 6 months worth of work to be done in 90 days I think the team probably would have quit. They were mostly contractors so paid hourly, so they got paid for all the work, but that's still a lot of hours for that many weeks in a row.

I have been very lucky not to come across anything like that yet.