Litter boxes should be changed every 2-3 days anyways, just for sanitary reasons. Even if there is a grate or mesh separating the bun from the litter, they can still get urinary infections and other hygiene related issues if the boxes aren’t cleaned every few days. For smell prevention, you can use wood stove pellets as litter. It’s very absorbent for easy cleanup and it stops most of the smell. You can also spritz a little vinegar in the boxes to get rid of any smells. 

I don’t think any rabbit owner can go longer than 2-3 without cleaning out the litter box because of the exorbitant amount of poop and pee rabbits expel on a daily basis, as A&B says, not based on smell, but for general hygiene.

A splash of apple cider vinegar (with the mother, if possible) in their water bowl will help reduce urine smell as well. Just a lil’ bit.

I don’t think you need to “wash” a litterbox every time. If you find the urine is soaking/damaging the bottom, you can either change the litter box more frequently so the urine doesn’t have that much time to set in on the litterbox floor, or line the bottom with something you can dispose of afterwards instead of washing. My preference is the former because as great as puppy pee pads are, they build up to a lot of trash.

I wouldn’t leave my rabbit’s litter trays for 3 days. The amount of poop and pee that would accumulate would be…disgusting. I change them daily.

I change every 2-3 days and I just have one bun and she has two boxes for herself. It’s quite unsanitary to let it wait any longer than that.

As others have said, it should be changed every 2-3 days anyhow. Aside from sanitary reasons it’s also important for their health. Flies can lay eggs in their litter, which can lead to flystrike. Especially during summers or when you’re living in a warmer climate it’s a major health risk.

I use wood pellets and it does a pretty good job at masking odour, however I still clean it daily (or max 2-3 days) because there’s simply too much poop and pee inside. Not because of the odour but because the box would literally overflow with poop and soiled litter.

Like the others, I change Panda and Fernando’s litter (Carefresh) every 48 to 72 hours, and wipe out the litterbox with white vinegar every Saturday. The buns tend to pee on one specific side of the litterbox, so there’s rather gross residue at the bottom on that side that I have to knock or scrape out when cleaning the box. They’re pretty good about pooping in the box but I always find “cocoa puffs” scattered around the lower level floor, particularly around their food bowls, and there always also seem to be a few on the floor in their play area. Rabbit poops (as opposed to cecotropes) are about as un-yucky on the scale as poops can get, though, so you can just pick them up and throw them back into the litterbox when you find them.

Because my Bun is a digger and litter kicker, I use as little litter as possible. She also loves clearing most of the real estate in her litter box bare for herself and just leaves 3 of the 4 corners with little mounds of litter. So, due to the lower amount of litter in her box, I like to clean it morning and night. As others have stated, I clean it this often, not so much for the smell, but just because rabbits really can do a lot of bunny business in there and I don’t really want it to pile up. As for stretching litter out more? This problem is resolved for me due to the above mentioned! Also, Bun tends to go in just one specific corner and when that is used up, I clear that corner, give a good paper towel wipe down and then shift the cleaner litter from a different corner over to the busy corner. This also helps save litter! And my budget!