Maia took about three days to learn to use a box as a baby. For awhile, we lived with a veritable sea of litter boxes, but now use just two. In another article, I will address the pros and cons of the bewildering array of litter products that are available for rabbits. For now, avoid softwood shavings such as pine or cedar chips as they emit gasses that cause liver damage in rabbits. Also avoid clumping or dusty cat litters as these can be fatal if ingested or inhaled.
Some people use only hay or newspaper as litter, and some litters can be flushed or composted.
Experiment to see what you and your rabbit prefer. Litter boxes should be cleaned often, at least once a week. White vinegar is excellent to rinse boxes out because it controls odor, kills bacteria, and is completely safe. All rabbits will drop a few pills around their cages and boxes to mark them as their own. It is very important to remember that this is not failure to be litter-trained.