Board Thread:Legitimate Canon Questions/@comment-26829181-20170225215737/@comment-4091815-20170227034255

Season 5 began with the start of senior year. Season 6 began with the final semester of senior year.

There's no confirmed timeline for Season 5. We can guess it takes place over a few weeks, since that's average for a normal story arc. We also didn't see Halloween or any other holiday to mark the passage of time, but lets call Season 5 "Fall."

Stiles went missing roughly three months before graduation. Let's call Season 6 "Spring."

That would mean there may have been several months between but there's little to say how many.