You can wear a wet diaper for an entire day or 24 hours.
I go sometimes 24 hours in the same wet diaper when I'm wearing a really absorbent adult diaper because I love the squishy wet feeling.
If the diaper however starts smelling of ammonia then the pee is turning to ammonia and can cause a rash so by then it's time to change the diaper.
I don't recommend you stay in the same wet diaper for 24 hours but I have without any issues.
The worse thing that would happen is you get a diaper rash.
It's best however to change your adult diaper every 3 hours or so just like a baby or toddler would have their diapers changed every 2 to 3 hours.
At night babies and toddlers can go up to 12 hours wearing the same wet diaper so adults can too.
If you start feeling a slight burning sensation on your skin or private areas then it's time to change.