A Clinton win or a Trump surprise: A viewer's guide to election night in America

When Americans cast their ballots today, the polls suggest they will probably elect Hillary Clinton as their next president. But the margin between her and Donald Trump remains narrow enough that the outcome might not be clear until late into the evening or even early morning.

So how might the night unfold in either scenario?

According to Monday's update of the Presidential Poll Tracker, Clinton holds a three-point lead over Trump nationally. That margin has held firm over the past week, suggesting Americans' views of the two candidates may have crystallized in these final days.

(Check out the Presidential Poll Tracker for the latest numbers, including the final polls of the campaign.)

Clinton's advantage in the electoral college has also held steady. The Democratic candidate is projected to be ahead in states totaling 323 electoral votes, with Trump winning the remaining 215 votes.

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In order for Trump to get over the 270-vote mark needed to win the presidency, he would have to beat his polls in the key swing states by about four points. The odds of that happening, based on past polling error, is only about 13 per cent about the odds of losing a game of Russian Roulette.

But when will Americans, and the rest of the world, know?

Based on where the polls are today and using the 2012 election as a guide for the length of time it takes to call states, let's game out how a Clinton win (as projected in the polls) and a Trump win (if he wins the swing states he needs) might play out.

(All times below are Eastern.)

8 P.M.: Safe states begin to be called

By 8 p.m., the polls will have been closed in a number of states for at least an hour. Based on exit polls and early results, many of these states will be projected by the major networks immediately: Connecticut, Delaware, Maryland, Massachusetts, New Jersey, Rhode Island, Illinois, Vermont and Washington, D.C.for Clinton; and Alabama, Indiana, Kentucky, Mississippi, Oklahoma, Tennessee and West Virginia for Trump.

That would put Clinton ahead at this stagewith 75 electoral college votes to 57 for Trump.

9 P.M.: Clinton orTrump advantage emerging

An hour later, hints will likely emerge about whether the night is leaning towards Clinton or Trump, though the networks will hold off on calling swing states like Florida or Ohio(where polls close between 7 and 7:30 p.m.) until more votes are counted.

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But indications of turnout could provide some clues: if Hispanics and African-Americans are voting in big numbers, then Clinton will be in a strong position. If not, Trump could pull off some upsets, particularly in states like North Carolina and Michigan.

The networks will likely be making other calls by this hour, however. For Clinton, New York would likely be called as soon as the polls close at 9 p.m. Virginia and Maine, where polls closeearlier in the night, might be projected for Clinton as well.

Arkansas, Kansas, Louisiana, Nebraska, South Dakota and Wyoming will likely be called for Trump immediately. South Carolina and Missouri might also be projected for the Republican by now if Clinton is not heading for a landslide.

That puts Clinton's tally at 121electoral college votes to 107 for Trump.

10 P.M.: Other states fall into place

At this hour, the networks might be comfortable making calls in some other states where the polls had closed earlier: New Hampshire for Clinton and Georgia, Montana and Texas for Trump.

According to this count, Trump would be ahead in the electoral college count with 164 votes to 125 for Clinton.

11 P.M.: Clinton approaches 270

If the night has played out as described, Clinton will move closer to 270 electoral college votes at this point in the evening. That is because states like Pennsylvania, Minnesota, New Mexico and Wisconsin could be called for her (or, if the networks are holding off or calling these for Trump, he is likely going to be the president).

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In addition, California, Hawaii and Washington might be called for heras well, pushing her up to 241 electoral college votes.

This is where Trump could fall further behind. The 55 votes in California tiltthe scale dramatically in Clinton's favour, while Idaho, North Dakota and Utah are together only worth 13votes. That bumps Trump up to 177.

If Clinton is on her way to winning, she will be leading in the swing states that have yet to be called. But the night will be far from over if Trump is leading in some of the remaining swing states.

12 A.M.: Clinton wins or things tilt to Trump

At this hour, if Clinton is on track to win, the networks are likely approaching a final call, if one has not already been made. If Colorado, Michigan and Oregon are now called for Clinton, that will put her at 273 electoral college votes. She will have won, with a number of states yet to be called.

On the Republican side, Alaska, Arizona and Iowa might be called for Trump. This increases his vote total to 197.

But what if the night is going Trump's way? His path involves turnout among white voters beingup and black votersstaying home. That could help Trump in a rust-belt state like Michigan. If he wins it, Clinton's electoral college vote stalls at 257 and Trump jumps to 213.

After midnight: Clinton victory speech or Trump's endgame

If Clinton has already surpassed the 270 mark, the outcome in states like Florida, Nevada, North Carolina and Ohio will be far less relevant.

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But if Clinton hasn't reached 270, it could be well past midnight before calls can be made in these swing states to decide the final outcome. Still, if Trump has picked up no other states than the ones listed above, he will need to prevailin all three of Florida, North Carolina and Ohio to come out on top. A Clinton win in any of these would sink him.

Barring a massive failure in the polls and an unexpectedly large surge in turnout among the demographics that favour Trump, a squeaker-win by the Republican nominee is the best he can hope for. The early signs of that happening may emerge early in the night but likely won't be confirmed until the next morning.

After a roller-coaster of an election, however, the networks may be wise to exercisean abundance of caution beforecalling it for either candidate.