Newborns will usually need 10 to 12 diaper changes per day. As they get older the diaper changes will happen less often and changing a diaper every 2 to 3 hours should be sufficient to keep your baby or toddler clean and dry enough.
Never go longer than 3 hours without changing a diaper or you'll risk giving your child diaper rash or yeast infections.
It's okay to let the toddler sleep overnight though without changing the diaper. But as soon as the baby or toddler wakes up the diaper should be changed.
You should also put a fresh clean diaper on your baby or toddler before going to bed for the night.