If they are different sexes, and you don't know when they started humping you would need to securely seperate them now, she might be pregnant and the buck would impregnate her again right after giving birth, and you'll end up wading knee deep in rabbits quickly.
If they are both male, it would be wise to seperate, humping is not a good sign then and the situation can escalate into a serious fight in seconds, they can severly injure each other.
If they are both female, humping is a normal part of their social behaviour, then I would arrange their space so that they can get out of each others eyes if they feel like it (avoid creating any dead ends) and keep an eye on that, how they react etc.
Seperationg part time is in none of any of those combinations a good idea, most likely creates way more problems than it solves.