The official 007 website has added a countdown timer to the teaser trailer due on Saturday, which reveals it will be available to view in the early hours of Saturday morning.
At the time of writing the clock is set to 2 days 5 hours and 28 minutes, which by my calculations means it will be released at
midnight Central European Time on Saturday, which is 11pm GMT on Friday 1am Saturday Central European Time on Saturday, which is midnight GMT.
Obviously that situation may well change, so keep an eye out on the countdown clock.
UPDATE: the official 007 Twitter account has announced it will be released at 11.45pm GMT on Friday.