If I may jump in rather late,
Aren't we rather missing the point in trying to determine a date for this 'devotion'? Who cares if it was pre- or post-schism? Arius' teachings were all pre-schism, it doesn't make them instantly Orthodox.
The Roman Catholics' schism was not one sudden action that severed their ties with Holy Orthodoxy, it was a series of things culminating in the schism. We should not look at whether or not something existed pre- or post-schism, but whether it is Orthodox or not. It should go without saying that it is only Orthodox themselves who are qualified to make that judgement, and so it is curious that Roman Catholics are so prevalent on a board about Orthodoxy to defend their own actions. This thread on the sacred heart has nothing to do with you, if you want to go to First Friday Masses go do it and let us to determine amongst ourselves what belongs in the future of The Church. For a group who supposedly doesn't care what we do there is certainly a lot of (often vicious, and directed at Clergy no less) rhetoric devoted to it by your side on this thread.
Western Orthodoxy, IMO, should not be about setting the clock back and trying to act as though we're beginning a step in 1053 and ending it in 2011. It must acknowledge the gap and not accept something just because it is Western or pre-schism, but truly filter everything through the lens of Truth. The best of (and I believe in the majority from what I've seen) WRO do just this. Our brothers and sisters in the west began veering away from Orthodoxy long before the schism. Our Western brothers and sisters now should take care, and not fear to reform (while obviously still staying true to their Western patrimony) their current liturgies and practices so as to ensure the security of the Holy Orthodox faith, which is truly the responsibility of all Orthodox Christians.