They won't sell it early, the reason being this scenario:
-so, they sell it early on the night before (tonight), and they sell out/sell most of the stock.
-People arrive early the next morning, queue for several hours (having being told already by Apple that they go on sale on the morning of 28th) -but there is no stock left. Riot ensues. Apple get a ton of bad press for lying to their customers, blah blah.... you get the idea 😉