There's nothing unusual about the the VP nominee speaking on Wednesday. That's when they *normally* speak, at least in recent years. Both Edwards and Cheney spoke at their respective 2004 conventions on Wednesday.
Um?
The point isn't that "Wednesday" means anything in and of itself, but rather that the theme for Wednesday is "national security/veterans affairs" and having someone with no experience on either of those issues would create a horrible mismatch. Sebelius indicated that the VP pick would have something to do with that theme.
The article makes statements like "There must be a reason for the VP candidate speaking on Wednesday" as if that's a big mystery. There is no mystery. Wednesday is the normal day for the VP nominee to speak. We already could have guessed that the VP nominee will speak that day. We also already knew what Wednesday's theme was. That was the source of the Clark buzz.