Here's something I noticed while watching "316" a 2nd time...
The first scene in episode "316", when Hurley, Jack and Kate find themselves back on the island, is 46 hours after the scene in the Lamp Post station.
There's nothing ambiguous about this-- the caption "46 Hours Earlier" appears between the opening island scene and the scene in the Lamp Post station. It's in this scene that Eloise Hawking tells Jack that the "window" back to island closes in 36 hours.
So why the 10+ hour discrepancy? why would they land on the island 10 hours after the supposed "window" has closed? I don't really have any theories, dumb or otherwise, I just don't think there would be this discrepancy unless it has some future bearing on the plot. Otherwise why wouldn't the caption be "36 Hours Earlier", or 27, or 32, etc.?
Eloise told Jack that something "unpredictable" could happen if the circumstances that brought them to the island in the first place weren't recreated to the best of their ability. We can't even be entirely sure yet what the predictable results should have been-- but I have a feeling that landing back in the 70's or 80's, or whenever Jack, Kate and Hurley are, wasn't the intended result.