Good lord!
Ok
It's not JUST the wetness. It's the bacteria and fungi (yes fungi!) that then thrives in wet, warm areas leading to nappy rash. Especially when they're awake and mobile which even newborns are, kicking legs etc that means friction too
Your aim is to prevent rather than have to treat nappy rash because by the time they have that (or a worse infection!) they are in constant burning pain.
It can take weeks to treat fully.
3 hours is too long during the day.
I mean, why don't you wet yourself @Husbandno4 and see how long you like sitting in it
And see how the nappy rash feels! Especially if where you are right now is experiencing hot weather!
Another reason to change regularly is so that you can note approximately if the nappies are wet enough and colour of fresh urine because again in this hot weather babies can be at risk of dehydration and again it's better to prevent based on early indicators than wait until there are serious symptoms
I would say no longer than 2 hours in the day as a rough guideline but also heed baby's cues, they'll fuss if they're uncomfortable and you definitely shouldn't delay if that's the case.