How often do they poo?

Here's my dilema, my fiance and i purchased a double het albino boa 2 weeks ago, on the second day of having him he defacated. I spoke with the gentlemen that sold us Kronos and asked him what he was feeding him, he replied mice. So i go to pet bazaar and i questioned it because Kronos is 8 months old and about 2 and a half feet long, they said i could give kronos a rat pup cause a mice was not sufficient. So i did, i got the rat pup and of course he took it down like a champ!! but he has not had a bowel movement.
So last week i go back to pet bazaar and like dumbass i got him another rat pup, but guess what! still nothing i've checked all over the bedding and nothing, so today i decided to run a warm bath for kronos to see if that would help him drop a deuce!!. Now tommorrow is feeding time and this time i'm going to get him a mice, cause i'm thinking his digestive system cant handle rat pups just yet. Any ideas cause i'm a bit worried is not like i can give kronos a laxative or anything. Please help