From Birthmarks, I gauged them at knowing one another for 17 years. But mind you, that's just my interpretation. I could be wrong.

And I have been before. I've taken information the show has given me and drawn conclusions, only to have them air another episode which basically contradicted what they'd established.

So I guess what I'm saying is, however long you want them to have known each other, is good enough.

Except putting them together in med school, which people seem to want to do and is basically impossible, due to their age difference.