theres nothing to stop you trying from birth, whether it works is another matter.
My son pretty much fell into a routine of 4 hourly feeds from birth but he was a hefty 9lbs 6oz so probably didnt need to demand feed, plus he was bottle fed which is differerent to breast feeding. he fed, and then slept for a couple of hours.
He then gradually dropped his night feed himself over the next 8 weeks.
I dont think at 5 weeks Id have made him wait for a feed though or forced him into any strict routine, he was a pretty easy going baby.