As far as I can tell, having observed this question closely if intermittently for 20 years, those 80-90 hour work weeks are a myth. Which is unsurprising, since self-reported data is famously unreliable.

There's never any independent evidence, and to the extent that you can test the claims, they don't hold up. For example, if you look in the parking lots of these buildings at night or look for which office windows have lights on, it's obvious that they're nearly all empty, and that's always been the case. But both sides in the argument ("yeah I worked that hard" vs. "no one should work that hard") have an incentive to agree on inflated numbers, so they can argue about the rest.

I do remember one startup where the CEO would have a tantrum if someone left before midnight, but that was only for a brief period (the situation was unstable), and even at the peak of that insanity, no one worked close to 80-90 hours a week. People would just come in late the next day. They certainly thought they were working 80 hours though.