If the baby has just wet once or twice then it's not bad to leave the baby in the wet diaper for a few hours until they fill the diaper up more.
Diapers are really absorbent and if you remove the child's diaper when soaked the skin will be barely wet or not even wet at all.
The diapers use SAP to absorb the urine and pull it away from the kids skin so they stay dry and not wet like they would with cloth diapers.
But if you're using cloth diapers and not disposable diapers then change the cloth diapers after you notice they are wet.
The cloth diapers don't absorb as good as disposable diapers do so change the cloth diapers more often.
You should check your babies diaper at least once an hour or every 2 hours to see how wet it is and if it's really wet it needs changed and if not then you can leave it on them for awhile longer.
You don't want to leave the diaper on too long though otherwise it could leak on their clothes or furniture.
Some older kids that are 2 or 3 years old may only need a diaper change every 3 to 4 hours and with super absorbent disposable diapers they may only need 3 or 5 diapers per day.