For me (as a programmer) it really varies a ton. I used to put in insane stretches, due to the medication I needed to take in the past and that is how I got used to things in college.
Now I work more regularly, but still can put in a solid 6+ hr day most of the time, and yet some days… yeesh I’m lucky if I can get a third of that. So I work more on other days to compensate.
Sometimes I only have 2 hours of meetings but they are all 30 minute meetings with an hour or two between. So I am barely back in my flow by the time he next meeting rolls around.
The “flow” thing is what most non-IT folks don’t understand. It’s tough to jump back in and just start solving the same puzzle I was working on hours ago with no backtracking to figure out which micro piece of the 20 regular-sized pieces I was working on.
That’s probably why I would procrastinate on technical work with project management work back when I was in IT.
Sometimes when I really get into something, I just stay late and work on it while the office is empty.
Thankfully I’ve been in positions where if I work the rare 10-12 hour day, I can take the time off later in that timesheet cycle. It helps that I always have a bunch of results to show after those nights.