HI Weirdly, no trash mobs or bosses respawn after been killed. Two hours after the first kills at the entrance, the zone is still empty.
IIRC the bosses and placeholders re-spawned a lot faster back in the day. Gods I remember camping all of them for the Claymore updates. Was it 12-13 years ago? haha! And then the Philosophers..... not only had to wait for re-pops, but 9 out of 10 the re-pop was just placeholders. I miss those days... more simpler and straight forward. Claymore was a long insane slog... but it was a well round progression from solo to group to raiding.
Speaking about the philosophers, 30mn and no respawn. When I did the quest a few years ago with my previous main, it was definitely much faster.