Hello Reldon, welcome to the forums! So glad you're enjoying the game!
"When it's done" is roughly what we've got right now for those.

Our aim is to release them with no larger a gap than we had between Episodes 1 and 2 (3 months), but exact dates are still TBD at this point. We'll be plastering the site with those dates when we've got them, though, fear not--it'll be hard to miss! PLus if you've ordered the season pass, you'll be notified via email when they're out as well.