I don't think that FFG has officially said anything regarding this certain topic, but speculation is fun .

I think that time period 1 might be Clone Wars, considering that we are currently in time period 3 that is right after ANH.

Period 2 would be in the time before ANH and after ROTS.

Four would be Empire to Jedi

etc...

7 would either be Leagcy or The Force Awakens

I highly doubt (and hope) we'll see anything during the Clone Wars, as that would elimate almost all of the figures in the core game (all of the imperials and all the rebel heroes.)

Plus Darth Vader is time period 1-6. And he didn't become mainly machine till the end of the clone wars. I think its safe to say that most of the time periods will be during the original 3 movies. Time period 7 might be after Return of the Jedi but I doubt Force Awakens (as that takes 30 years after and once again, eliminates alot of the core figures.)

Basically, the way the game is set up, you have to consider what time period the figures existed in and what time periods the unique characters are available in.

Yeah, I think (personally) that the time period criteria isn't meant to do anything except reflect the time period covered in this game, and that too many folks are reading too much into it. Sometimes a cigar IS just a cigar.

Here's some time period speculations from BGG http://boardgamegeek.com/article/17859212#17859212 that might interest you.