Silver calculates them:
Our model estimates that while Republicans have a 64 percent chance of winning the Senate eventually, there’s only a 27 percent chance they’ll be able to claim their victory within the first 24 hours or so after polls close on Nov 4. Democrats are even less likely to win a quick victory — they have just a 12 percent chance. The other 60 percent of the time, it will take days or weeks to sort everything out. The chart [above] lists the states that are the biggest part of the problem.