A 1 year old baby will need his/her diaper changed every 1 hour to 2 hours depending on how much they drink.
The more the 1 year old drinks the more they will need to pee and the more often you'll need to change the diaper.
You don't have to change the 1 year old babies diaper right after they pee because disposable diapers can and do hold a good amount of pee and absorb it to keep it away from the babies skin.
So the baby can pee between 2 and 3 times before the diaper gets full enough to need changed.
You can feel the diaper with your hand and see if it's squishy enough to need changed and if the diaper becomes squishy then you should probably change it.
As the baby gets old they will usually need less diaper changes less often and sometimes a 2 year old or 3 year old can go up to 3 hours before they need a diaper change.
When the baby gets older they will usually hold in their pee and let it all out at a set schedule.
If the toddler poops then you should change it as soon as you notice but you should wait at least 10 minutes or so before you change the poop diaper.
If you try to change the poop diaper too soon then the baby or toddler could poop a few minutes after and then you could get poop on you or need to change the diaper right after again.
So allow the baby or toddler at least 10 minutes before changing the poop diaper.
When I had kids in diapers and they pooped within 30 minutes of bath time I would just wait until the 30 minutes has passed while I got the bath ready.
Because 30 minutes in a poop diaper is not gonna harm the baby because my kids slept in diapers that they pooped in.
So they were likely sleeping in the poop diaper for 8 to 10 hours depending on when they pooped the diaper.