I'm going to be positive and say tonight. This event has been advertised and trailed a HUGE amount over the past few days, which suggests Sony want all eyes on it. There's an expectation of pre-orders, and I can see them fulfiling that expectation.
I would hope that you could after the showcase with some communication beforehand to say so. But they dont need to worry they have their own plans and probably havent changed them (apart from maybe price). So im going with after 22nd Sept. But you know im prob wrong.