Pediatricians recommend changing diapers every two hours, and even more frequently if needed. The urine consists of ammonia, which is caustic when the baby's little bum gets soaked in it for hours. So it is good to change the diaper as frequently as needed and wipe the baby well. If the baby has soiled the diaper, then wipe of any feces and then wipe again with a new wipe. Even it is just urine, wash it off.