I may get hate mail over this answer but for several years now I have left my buns alone for up to one week. I wouldn't feel comfortable leaving them any longer than one week. Here's how I do it: I place 6-7 water bottles attached to their pen. I have an automatic pellet feeder (cat-dog feeder) that dispenses the proper amount of food daily. I leave several boxes of fresh hay attached to the side of their pen with a square slot at the bottom front of the box to allow them to pull hay out of the box as they eat. The hay will naturally slide down the inside of the box due to gravity as they consume it from the box. I also have a web cam set up so I can watch them on my laptop where ever I go. We do have an animal loving neighbor who has a house key that will come in if I think anything may be amiss when I look at them through the web cam. So far the buns do well with this arrangement and when we come home they look at us as if to say hohum I see you're back again. ( A little deflating as dogs would dance around in excitement as seeing their owners return!)
BTW our buns are small (3-4 lbs) each.