Managers actually plan, and stop relying on it. Crunch time is not something that should exist, as it's just punishing employees for the inability of management to make a sane schedule.
At most companies "crunch time" is just a label stuck on "squeezing salaried employees for every last drop of juice".
When there's no penalty on the company for needing crunch time, suddenly they find themselves needing a lot of it.
You can easily see how nonsensical all of this corporate garbage is by hypothetically flipping it around to the benefit of employees and think about how they would react instead.
Hey boss it's "quiet time" can I go home an hour early for 2 weeks? No ... DING DING!
So don't expect it to be ok to ask me to stay an hour late because it's "crunch time".
Same thing applies to "as long as shit gets done". They always adjust that so that somehow the amount of shit that is expected to get done is more than you can manage in a day. Never the other way around.
No company says "hey enough shit got done for today and it's 3PM so go home and see you tomorrow". No in that case you keep working and get more shit done.
Let's not dress it up, it's all corporate psychological warfare.
My current employer though? If we had crunch time and then told my boss I was gonna go home an hour early and do 4 days a week for the next 2 weeks to make up for it? No brainer, they'll say yes. It's also not that uncommon for managers to send people home if they shipped a lot of stuff that day.
I'm a manager myself, and I frequently had to have the talk with my reports to tone it down. The last thing I want is burnt out employees. I've actively told some to calm down and work less.
Which for an individual totally works and solves the problem. Just trust. Unfortunately people also like fairness in pay and compensation...and that start making things tricky.
Changing from that fluid "as long as shit gets done" schedule to a specific "you now work for days" gets really weird to me. Do I have to work at least 4 days now? What happens with crunch time? What happens if there's an emergency and I end up working on the 5th day, do I get overtime?
Then what happens during perf review? there's already a 500% difference in output between 2 random engineers, and it's already hard to figure out if they're just better, working longer, or what. Comparing the output of a 4 day/week vs a 5 day/week one to make sure the former doesn't get penalized gets tricky.
I mean, if it works at the likes of Google, so I assume people have the answers to these questions. I'm genuinely curious.