Conversely, I’ve never once had to punch a time clock at any of my salaried positions.

None of my employers would ever be able to tell the difference between 38, 39, 40, or 41 hours in any given week (nor has any given any indication they'd care even if I told them the difference).

I have worked primarily for the prime contractor on Department of Navy work. Either at a prime ship repair yard or an AIT. They take time cards very seriously. I'd suspect you might get some wiggle room in the public realm/software, but as someone mentioned below I'd prefer my time/money trade to be explicitly laid out.