if I use the snooze button in the conversation window, where we get a drop-down menu, it works as it should. I'll snooze for the duration chosen.
However, we can also set up a default snooze duration for group chats in the group information window. I had thought that right-clicking the group and choosing "snooze session" would use the setting for the group, instead it defaults to always doing 20min.
I kinda doubt that's planned behaviour.