Ninja Theory just confirmed what time the demo will be hitting. Approximately 12 GMT.
"It’s Thursday!
At some point today (possibly around lunchtime GMT) the Heavenly Sword demo will finally make it’s way onto the Playstation Network. This here is the thread for impressions, feedback, comments etc etc.
Hope you guys have as much fun playing it as we’ve had making it!"
Source: NinjaTheory Forums