You should change a baby or toddlers poopy diaper in the middle of the night as the baby or toddler could get a rash or even urinary tract infection from the poop.
The risk of getting a urinary tract infection from poop is higher for baby girls than it is for boys although both boys and girls can get a urinary tract infection from poopy diapers.
I would always change my baby or toddlers diapers at night when they have poop in them, but the pee can wait until morning unless the wet diaper is bothering the baby or toddler.
I once made the mistake of letting my 2 year old son sleep in a poopy diaper all night because I was too tired to bother changing it and he was sleeping good.
However he later got a bad diaper rash and also got a urinary tract infection that almost went to his kidneys and he was even peeing out blood.
He had to take antibiotics for it and if not treated it could've lead to kidney failure.
So yes always change a poopy diaper as soon as possible.
If your child or baby will wake up within 30 minutes then it's not as big of a deal but it's best to change the poopy diaper as soon as possible.