Ed Kilgore has a guide:
The first big hint of what's to come will be at around 5:45 p.m., when media outlets begin reporting partial exit-poll data about the makeup of the electorate. These news organizations actually receive all the exit-poll data that is available around the country at 5:00 p.m., but they don't use it to call races until polls close in the relevant states. Yet they are willing to report the non-candidate data from the exits earlier in the evening--and, if you read it right, that information can tell you a lot about who's going to win.
The first polls close in Kentucky and Indiana at 6 pm:
There are three House bellwethers in Indiana and Kentucky that bear close watching: IN-9, a perennially marginal district, where Democrat Blue Dog Baron Hill is a slight underdog to Republican Todd Young; IN-2, where a Class of 2006 Blue Dog Democrat, Joe Donnelly, is in a very close race with Jackie Walorski; and Lexington-based KY-6, where still another Blue Dog Democrat, Ben Chandler, who took the seat away from the GOP in a 2004 special election, is in a tough race with Andy Barr. This contest will say something about whether a candidate who voted for climate-change legislation can survive in a coal-producing state. If the GOP sweeps these bellwether districts, the odds are very high Republicans will control the House and could well exceed the 54 seats won in 1994.