I still see things from 7 days ago at the top when I sort by “active” while other posts have much more activity and are newer. “hot” is the same thing with most posts from 5 days ago.
On https://lemmy.ml/ and https://lemmy.world/ it seems like sorting by “active” is working, there are posts from around 3h ago that have 100 upvotes so that I would consider “active”.
I believe hot is the only ranking that runs as a scheduled task, as it is uniquely expensive to compute. I believe others are updated in real-time. It’s possible I’m mistaken, but I’ve been watching a few GitHub issues and this is the impression I got from dev discussion there.