Here’s the schedule for Tuesday, February 16 (in the U.S.):
8:00 PM — Rerun of 6×03 What Kate Does. This is, presumably, going to be the enhanced version, with the pop-up hints.
9:00 PM — New episode: 6×04 The Substitute. From the sneak peeks (here: warning spoiler-ish, and here), this looks like it is going to be an amazing episode. Also, ABC hasn’t put an episode summary on their schedule, the way they usually do, so I think they may have some big surprises in store this week that they are trying to keep under wraps. So exciting!
(Show times, as always, will be an hour earlier in the Central Time zone.)
Screencap of Locke (or, more likely, notLocke) is from sneak peek #2.