I have beaked snakes and dispholidines that will process a prey item in less than 30 hours. Same with psammophylax and philodryas spp. But these area active, quick moving snakes - even in captivity.
Drymarchon, if offered a thermoregulation zone will poop within a few days of feeding.
Ball pythons poop slow...they move slow and once their husbandry needs are met, move very rarely. I'd argue that even without a study, we can say they have at least a slower metabolism than many other species.
What I'd like to see if a study regarding the efficiency of the metabolism of ball pythons. In south american colubrids, that efficiency is about 50%. In some african colubrids, that number goes up a few points. Never seen one on ball pythons...