There is no schedule, snakes in general are very efficient and bowel movements may vary from once a week to every 4 to 8 weeks. It depends on feeding frequency and prey size as well as metabolism (older animals having a slower metabolism)
Young animals utilize a lot of their prey for growth as well so that is to be kept in mind.
Unless there are signs of an obvious blockage which would be a persistent bulge near the cloaca there is nothing to worry about.