A toddler will need a diaper change ever 2 to 3 hours depending on their age and how much they pee or poop.
If the toddler poops in their diaper you should change the poop diaper within 5 or 10 minutes after the toddler poops in the diaper to avoid rashes.
If the toddler is just wet then you can wait up to 3 hours before changing the wet diaper because diapers today are very absorbent and can hold a lot of pee.
The diapers also hold the wetness away from the toddlers skin so they don't feel very wet at all anyway.
Some toddlers may pee more often than others and some toddlers will hold their pee in and let it all out at once so you may notice a schedule when the toddler pees or poops and needs changed.
I would check the toddlers diaper every 2 hours to see if it's wet enough to need change but sometimes you can wait up to 3 hours to change the toddlers diaper.
During the night you can let the toddler sleep through with a wet diaper and not worry about changing it.
But during the day when the toddler is awake make sure you're changing the toddlers diaper every 3 hours minimum but if the toddler is really wet after 2 hours then change it.