I don't think you need to worry about having too long chapters - all books are written differently, some have really short chapters, some have chapters that are hundreds of pages long. In my current novel, the chapters are really long as well, I don't see that as a problem. And I don't think it would be weird at all to first have two chapters in Jan, 2009 and then continue the story in Jan, 2014.
But I do think that if this prologue is going to be long, it's better to have it as its own chapter or a prologue than to have it as a flashback, because it seems to contain a lot of information, and I think it would be too much to have that as a flashback.
"I'm not lost, I just want you to find me"
Lost - Six60