It looks as though the first hard information from the exit polls will start emerging by about 5pm EST or 10 pm GMT and this should start to affect the betting fairly quickly.
This appeared on Slate an hour or so ago and gives a good guide to what is likely to happen.
As this item posts, the first raw exit poll data are streaming from the National Election Pool consortium owned by the Associated Press and the five television networks (CBS, ABC, NBC, Fox, and CNN) to their news divisions and to the newsrooms of NEP subscribers—big city newspapers and other broadcasters.
These early exit poll numbers do not divine the name of the winner. Instead, regard these numbers as a sportswriter does the line scores from the fourth inning of a baseball game. The leading team might win the game, but then again it might not. But having the early data in front of him helps the sportswriter plot the story he thinks he’ll need to write at game’s end.
As you read this posting, the political reporters at the networks, the New York Times, the Washington Post, the Los Angeles Times, NPR, Newsweek, and about two dozen other news outlets are cracking their knuckles over their keyboards, contemplating the story, while statisticians and political analysts at the networks prepare to run the numbers through their computer models to generate a prediction.
Slate have said that they will not follow the convention of keeping this information quiet – anything they have will be published.