Most 2 year old children will need a diaper change every 2 hours to 3 hours depending on how often they pee.
If they have a wet diaper every 2 to 3 hours in the day then the 2 year old is getting enough fluids and if they haven't had a wet diaper that is wet enough to need changed after 3 hours then they could be dehydrated and you would need to up their intake of fluids.
My children had wet diapers every 2 to 3 hours during the day when they were 2 and they would usually wet ever 2 hours or so depending on how much they drank.
I always kept my children hydrated and sometimes they would need a diaper change every 3 hours and sometimes they would need a diaper change every 2 hours.
I checked the 2 year olds diaper every 2 hours and sometimes it was wet enough to need changed and other times it was just a little wet so I would wait another hour and check them again.
Sometimes my 2 year old son would come and tell me when he was wet and needed changed and my other 2 year old son would not tell me and would stay in the wet diaper forever if possible.