According to All Feline Hospital, cats are capable of not urinating for somewhere between 24 and 48 hours, even if the cat has recently had food or water. Indoor cats should ideally have access to a litter box at all times to relieve themselves.
Cats' bladders are constantly working, so although a feline is capable of not urinating for 24 to 48 hours, it often urinates much more frequently. If a cat holds its urine for more than 48 to 72 hours, it may be at risk of serious injury or death as toxins build up. For travel, experts recommend that the cat be let out of the carrier to urinate at least every six hours.