We're still(!) waiting for the exact date to be confirmed. However, the British Film Institute will host a star-studded preview of the first episode on Friday, June 12 in London. (Wow, way to snub Wales.) And not to get too far ahead of myself, but that date seems to make June 15, the following Monday, the best candidate for CoE's transmission.
The BFI has also sent out a spoiler-lite summary of Episode 1:
1965: Twelve children are gathered on a deserted moor, before being surrounded by a harsh, bright light .... and then they are gone!
Today: all over Earth, children stop moving. Stop playing, stop laughing. Then, as one, they begin to speak with the same voice, announcing the imminent arrival of a new alien threat. "We are coming...". As the British government closes ranks, it issues a death warrant against Captain Jack and Torchwood...
(full news article here)