The Lightning-Speed Waltz

Hmm, I don't think "working overtime" is a concept in Starfleet. That would imply that people get paid, and get paid extra based on their hours. Starfleet officers do their jobs and take the time needed, while still (hopefully) maintaining a good work/life balance. Meanwhile, Starfleet takes care of all their needs. In a way, all Starfleet personnel are "volunteers." They work from a sense of duty, honor, and personal fulfillment. They don't ever have to worry about money or pay or hours.

Work/life balance is probably still a thing, and finding that right balance is something Starfleet no doubt encourages, at least in peacetime. A personally fulfilled, happy officer is a good officer in Starfleet's mind. I suspect in the Federation, superior officers probably have to encourage people to take leave or not work too much, since everyone loves their jobs, and maybe overdoes it on the work side of the work/life balance.

Hurray post-scarcity socialist space utopia!

Now, if overtime were a thing, I think most of the Starfleet characters on DS9 would work it without complaint. Bashir and Worf would do so without question. Sisko probably works himself to the bone, but he does make sure to carve out time for Jake, his friends, and for other R&R (baseball, cooking, building stuff). O'Brien would pull a ton of OT but probably gripe a bit. He likes to gripe. Griping is one of his hobbies.

The only possible exception, in my mind, would be Dax (both Jadzia and Ezri). Jadzia and Ezri both seem to value their private and recreational time and have very good work/life balance.