According to an official post on the Star Wars: The Old Republic Forums by BioWare's Stephen Reid, early access invites have gone out for all people who pre-ordered "up to the very beginning of October (roughly." Stephen notes that the same number of people will be invited for November, which should bring them up to the last week of November. Simple math (and boy am I bad at that) says that most early access preorders should therefore get in by the 17th or the 18th.

Stephen is warning players, however, that as more players are let into SWTOR's early access, while more servers will be coming online, "almost certainly there will be some queueing." Brace yourselves, the queues are coming!

You can read Stephen Reid's full update on the official SWTOR forums.