In my very limited experience (n = 1), hours per week is the same as anywhere else i've worked.
One quirk is that the trading day starts at seven in the morning, so at least one dev in the team has to be awake(-ish) and logged on to handle any technical issues. Before the pandemic, that meant being in the office, so an 05:45 alarm clock for me, but these days we do it from home. Another quirk is that trading winds down after six in the evening (exact time varies), and some releases have to wait until after that, so sometimes you've finished a piece of work but have to loiter to actually release it. Again, these days we can do that from home, so less of an impact, but still can be annoying.
Also, my team does its own out of hours support on a very unstructured basis, so you could get an alert in the middle of the night (but not weekends) you need to respond to, although this is rare (and is mostly in our hands to keep rare!).
I expect that better-organised teams have better ways with dealing with all this!
That's another load of BS spread by people not in the industry. They equate HFT's and quantitative hedge funds the same as investment banks. At most HFT's, mine included, devs are mostly doing 40-45 hours a week. Some places like Citadel, Headlands, the work hours are terrible (still not IB level bad), but the rest of the places it varies between 40-50.
