Never heard that but I'm sure it has nothing to do with the time,
More with the first few hours of sleep (being that most aticles are written for people working typical 9-5 and sleeping to accomodate that)
Of course the first few hours would be the most beneficial. that when the body is the furthest in its sleep dept. Also it could also be an attempt that getting the first few hours in on a regular basis helps the body regulate it sleep patterns.