A toddler does not need a diaper change until the diaper has filled up with pee.
There's no need to change a wet diaper just because they have peed once or twice.
If the diaper is a disposable diaper then the toddler won't even likely feel wet when they have wet the diaper a few times and so in reality the pee is not in contact with the toddlers skin.
So it's certainly okay to wait 2 to 4 hours for the toddlers diaper to fill up with pee before changing it.
With cloth diapers they feel wet so you should change cloth diapers within an hour or two of the toddler wetting the cloth diaper.
Disposable diapers it would be a waste to change the disposable diaper just because it has a little pee in it.
As long as you're changing the toddlers diaper ever 3 to 4 hours you're doing okay.
If the toddler poops the diaper then yes change it as soon as you notice it.
But pee can stay in a toddlers diaper for 4 hours and even sometimes as long as 6 hours depending on how often the toddler pees.
Some toddlers only pee every few hours and so they won't be as wet as others.
As the toddler gets older they tend to hold the pee in longer and then pee in the diaper every 2 to 3 hours.