My money's on tomorrow. Last 2 years it's been the 1st fri in july. Last year I was browsing the sale at 4 am with irregular contractions. Waters broke at 4.30, clicked on "checkout" in a bit of a panic and ended up with waaay too much stuff in bizarre sizes.
I assume it starts at midnight.
Kaloo - once I did that - the items were still in the stock in the sale - I called up and they adjusted the prices for me as they were still in stock. This was ac ouple of years ago, mind you - they may not be as accommodating now! But you could always order them again and return the full price ones. (I usually manage to have one or two spare returns labels knocking around when then send 2 by mistake! Was gutted when they moved their warehouse a year or so back as I had 4 labels I couldn't use any more!)