my mom and i also were confused b/c we also heard (vit c away from mms )12 hours and 4 hours... so i am not positive which lot of hours it actually is.
i read somewhere that mms can stay in the body up to 12 hours so that is why my mom chose to be on the safe side and stay as far apart as possible. she wanted mms to have the time to do as much as it can without possibly disturbing the mms process.
i am sure if you searched vit c and mms on this site or surfed around a bit on other mms sites (or looked carefully thru the mms book), you would find more specific info about mms and vit c.
---maybe idlesfireguy knows more. he seems to know alot.