They reviewed every single piece of code many, many times.
They were draconian about memory handling, loops, preprocessor directives, and recursion.
All functions had to check all return types from other functions.
No more than one level of pointer dereferencing.
All code bodies had to fit on a piece of paper.
/edit should add, they used their tools thoroughly: compilers were run on max warning levels and absolutely no warnings were accepted, ever. They also used several static analysis tools on the code (under-appreciated these days!).
None of this crunch time bullshit, though I'm sure it happened.
I've been on one of those binges. If another coder hadn't seen my errors, due to diminishing sleep, I'd probably keep banging my head against the wall. Just compounding the situation.
That doesn't mean the former finish first, they usually don't. But their code tends to be more thoughtfully constructed. They have a vested interest in not spending their time in the office, and that means minimizing debugging time along with coding time.
When you're in a hot field with lots of competition, maybe those sprints make sense. But in the field of NASA-type systems, there may be a deadline, but it's rarely urgent. This gives the developers much more time to step back, breathe, and think.
If you follow their other guidelines (no recursion, fixed sized loops, etc.), then it can take you several lines to do much of anything, so 60 isn't very long. Those things combined means you're basically saying that each function should only be attempting to do 2-3 significant things, which seems about right to me, as most people can't fully understand more than 3 things simultaneously at one go.
See page 4 for the rule summary.
https://www.amazon.com/gp/product/0201546647?ref%5F=sr%5F1%5...
And here's some further summary information and reading recommendations from Steve McConnell.