There really is no "time frame" for quarantining an animal. It's pretty much when you are sure the new addition is in good overall health. Sometimes that only takes a several weeks, and sometimes several months. You'll know when it's time. As far as distance, keep them as far away as possible, at least in a different room. You'll want to make sure that you wash your hands very well when going from the quarantined animal back to your collection. I would even go as far as changing clothes to. In the even that the new animal does have a mite infestation, it could spread from the snake, to your clothes then to your collection. Sounds a bit extreme but it would be much easier to do that rather than treating your whole collection.
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Hope that helped.