User blog comment:Alois-pyon/What's the deal with the number 7?/@comment-94.67.103.162-20111016140639/@comment-7418318-20130620223405

The timeskip wasn't really 7 full years. They disappeared in december and reappeared 3 month before the GMG (which started on the 1st July), which would put it in late March or early April.

So it's actually a little under 6 years and 4 month and probably even less for the anime, to fit in the KotSS arc.