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6:30 P.M. Polls close in three states, including all-important Ohio (18) and North Carolina (15). If Ohio is particularly close, there's a chance the outcome there won't be known until after Election Day, and the presidency could hinge on it.
In North Carolina, the most conservative of the swing states, Mitt Romney appeared to have the late edge in polling. A victory by President Obama, who narrowly won the state in 2008, could point to broader troubles for Romney.
7 P.M. Polls close in the District of Columbia and 16 states, including battlegrounds Florida (29) and New Hampshire (4).
Democratic-leaning parts of Florida tend to be the last places to report, so be careful about jumping to a conclusion if Romney looks strong early on. About 4.5 percent of votes weren't counted on election night in 2008, so if things are tight, no one's going to be hasty about declaring a victor.
Keep watch on Pennsylvania for any signs of a Romney surprise.
7:30 P.M. Polls close in Arkansas (6), where Romney is comfortably ahead in surveys.
8 P.M. Polls close in 14 states, including battlegrounds Colorado (9) and Wisconsin (10). Colorado, where almost 80 percent of voters cast early ballots, could be a straggler because it's so close. Historically, as much as 10 percent of its vote doesn't get counted on election night.
Also watch Minnesota and Michigan, states considered safe for Obama but where Romney has made late moves.
9 P.M. Polls close in four states, including the last of the battlegrounds, Iowa (6) and Nevada (6). Iowa's been leaning toward Obama, but watch how the vote breaks down geographically. Can Romney's advantage in GOP-heavy western Iowa overcome Obama's edge in eastern swing territory?
If Obama wins Ohio and Wisconsin, Romney would have to have help from the West, in places like Nevada and Colorado. A Romney win in Nevada would really mean something.
10 P.M. Polls close in five western states, but most are foregone conclusions for Obama. He gets 78 electoral votes from California, Hawaii, Oregon and Washington; Romney gets four from Idaho.
MIDNIGHT The last of the polls close, in Alaska. Romney gets three electoral votes.
Will many people will still be awake? Political junkies will likely be waiting to see how things play out in one or more battleground states.