This is for two reasons:
The first is that I set the original deadline, forgetting that I've got a family vacation starting in a few days, and will not have any chance to look at, or manage submissions until I'm back on the 25th.
Secondly, and more importantly, there is still room left. I've received some really great stories so far, but there's at least three days on the schedule left to fill. If the new deadline passes without enough submissions, even though I'll be bummed - I'll be cancelling the "show". I don't want to do disservice to the people that have submitted so far by doing the thing halfway, so all stories would be returned at that point.
But - that's a last resort. Last year's festival of psychological terror was an amazing gathering of authors, some new, and some that I already knew. From what I've received so far, this year could be even better - so spread the word, and get those "Unsettling" stories in!