As a very general guide, young corns will shed at around 4 week intervals assuming they have appropriate feed and temperature to digest efficiently.
(Slight side note) I suggest to keep a simple "log". Nothing fancy is needed, just a page from a note book that you write down the date you feed and what they ate (eg. 1 pinky), when they go into the blue phase, and when they shed, even when they refuse a meal. This may seem pointless at first, but you will build up data that will help you predict an oncoming shed. If nothing else this log may help explain why your snake may not eat (if it turns out to be one of those snakes that will refuse a meal when about to shed as some do). A log will also serve as a reminder of past activities and eliminates any "guess" work of remembering what happened 4,5 or 6 weeks ago and alert you to any potential problems.
Hope this helps some.