This news is not yet 100% official, but Che Chou(One of the leaders in Turn 10's crew) has written a post on the forzamotorsport.net forums.
The post is this: "Demo is definitely hitting tonight -- but it'll be pretty painful for east coasters.
Trying to pin down an exact time."
This mean that the demo will hopefully be out tonight.
So we can only hope and see!