I look at it htis way. First, re: Biden, his comment was I guess off the cuff, no one’s really counting him out, so I’m still thinking it will be Biden. What we do know is it won’t be Clinton because he’s said he wants his pick to be someone who’s in politics for the right reasons. I also don’t think he’s going to want to put a less experienced person who might be more “exciting” on the ticket…he brings enough excitement to the ticket by himself, so much so that he’s criticized left and right by McCain about being all flash and no substance…he needs someone that the skeptics will see as “seasoned” particularly on foreign policy. Biden just seems to fit the bill.
As for the timing, the smartest thing he can do is to dominate a full news cycle (the morning pre-work news circuit, the morning rush hour radio news circuit, the evening rush hour radio news circuit and the evening news in particular. It either makes sense for him to make his announcement around 8:30am eastern time so that it hits right in the middle of the morning news cycle on the east coast and right at the very front end of the rush hour on the west coast…it give everyone a full day to buzz about it at the water cooler, and then is still the top story on the evening news that night. Either that or he should do it about 5:30pm eastern time, so it breaks right at the begining of the evening news/in the middle of rush hour on the East coast and hits right before the start of rush hour on the west coast, then it gives the morning news programs time to prep for it to be the biggest story of the following day.
So, that leaves him 3 options, either 5:30ish this afternoon, 8:30ish tomorrow morning, or 5:30ish tomorrow afternoon. Those would be the STRONGEST times for him to announce, though technically it could come as they say “at any moment”. There’s something to be said for letting the suspense build as long as possible though, if they truly have a leakproof ship (and it appears they do), they’ve got everyone talking about it now, the fact that his annoucement is imminent has been near the top of the headlines almost every day since he said he was going to email and text it to his supporters, and the longer he waits, the more frenzied the speculation becomes.
For that reason, it might make sense for him to wait until 5:30 tomorrow evening. Thing is, he’s not going to want to wait until Friday morning, because come Friday afternoon, people are thinking of the weekend. The period between noon Friday and when the pundits hit the air on Sunday morning is a black hole for news coverage…that’s where you dump news you want to bury. Plus, he knows the news coverage from Friday afternoon through the Sunday morning talk shows will be all about him and his running mate and their Saturday appearance together, so he probably achieves maximum coverage by waiting until tomorrow afternoon.
The only way I can see him not doing it to maximize news coverage is if something about his pick is newsworthy enough to keep people talking anyway (like say, selecting a woman not named Hillary).