It's okay to leave a child in the same diaper for 6 hours as long as the diaper is not really soaking wet or poopy.
Diapers only need changed when they get full of pee or they have pooped in the diaper.
There's no need to change a diaper with just a little pee in it as diapers are very absorbent and the child in the diaper does not feel wet in the diaper unless the diaper is completely full.
When your kid pees in the diaper and you remove the diaper take your hand or finger and feel the inside of the diaper and you'll notice that you will likely not feel any of the pee on your hand.
That's because the diapers use SAP which absorbs and holds the pee away from the kids skin.
Cloth diapers feel wet but disposable diapers do not unless they are really wet.
I watch a 3 year old who only pees every few hours and so he can go up to 6 hours in the day without a diaper change because he holds his pee in for a few hours and then pees all at once.
Then he pees again 2 hours or so later and then again and then after the 3rd pee the diaper is full and he needs his diaper changed.
My 2 year old son can sometimes go as long as 6 hours without a diaper change unless he has pooped.
You still should check the diaper every 2 hours or so and change the diaper when needed.