Most daycare centers change a baby or toddlers diaper every 2 hours or at least check the diaper every 2 hours.
When I worked at a daycare center we had to change the babies 1 year old and under every 2 hours regardless if they were really wet and if they pooped we had to change the diaper right away.
With older kids in diapers such as above 2 years old we could get by with checking their diapers every 3 hours if needed since usually a 2 or 3 year old in diapers would wet their diaper less often and sometimes would hold the pee in and wet their diaper every few hours.
Disposable diapers hold a lot of pee so the toddler didn't even feel wet but after 3 hours we needed to change the toddlers diaper.
If the toddler pooped the diaper then it was time to change it whether or not they have just been changed a few minutes prior.
Sometimes we would get so busy that we would not get to a toddlers diaper with poop in it until 30 minutes later.
That is not too bad though as it's not gonna hurt them to stay in the poop diaper for 30 minutes but if we noticed sooner the toddler would get diaper changed right when we noticed.