I can respond to the first part: my job has a hard 40 hours per week but also flex time. They're not mutually exclusive. I can tell my colleagues that I'll be

I can respond to the first part: my job has a hard 40 hours per week but also flex time. They're not mutually exclusive. I can tell my colleagues that I'll be out for the rest of the day and make up the lost hours tomorrow. Conversely, I can work with them into the wee hours and work proportionally less time the rest of the week (it just has to add up to 40 on Friday). It's my first job, though, and I have no intuition about how common this arrangement is (or how alternatives even work; if there's no hourly cap mandated, how do you know how long to work???). :p