Nintendo's "Wii Prove our Promise" presentation at the Leipzig Games Convention will take place early August 23rd (4:15 a.m. EST). With no Space World and a promise to reveal launch details by the end of September, this seems like the likely platform for announcements.
And, if this memo is true, the clocks will likely be installed the same day, or earlier and then activated. Still, these "leaked memos" do nothing but incite fanboyism and instill generally false hope. The rumor derived from a post by an administrator on the Nintendo Wii Chat forum and quickly made its way to the top of Digg's gaming section. Don't get too caught up in the hype; while countdown clocks would be a smart marketing move, these rumors rarely work out.
The memo has been transcribed below, or you see the original scan here.