Atlantis launches later on mission STS117, to take things to the International Space Station. Launch time is scheduled to be 7.38 pm EDT.
I think this must be 00.38 BST tomorrow (Saturday). There are two countdown clocks on the NASA website. The one which I think is giving the actual time to launch is saying (at 2320 BST Friday) that there is 1 hour and 17 minutes to go. The other clock (saying 20 minutes or so) includes all the holds that take place in the countdown.
Anyway, I am watching on NASA TV, so will be able to tell you, if I am still awake!
There is mission information at http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts117/index.html with links to a blog (not active yet) and information about NASA-TV coverage. You can watch NASA-TV on the web.
>>Later additions - the blog is now active.