Voters will be casting their ballots all day — poll opening times vary locally, and indeed, all the residents of three tiny towns gathered to cast their ballots at midnight Tuesday. But polls will close for nearly all of the state at 7 pm Eastern, and a few straggler polling places will close at 8 pm Eastern.
Importantly, registered independents are permitted to vote in either of the two major party primaries (though not both). And residents who aren't registered to vote can register at the polls. If you live in New Hampshire, you can get more information on how to find your polling place here.
What to expect at the New Hampshire primary
Unlike in Iowa, recent polls in New Hampshire have all agreed on who's in first place in both contests — Donald Trump on the Republican side and Bernie Sanders on the Democratic side. Both hold big leads in polls, so at this point they're expected to win their respective primaries. But a sudden swing to another candidate can't be ruled out. Many New Hampshire voters make up their minds quite late, Hillary Clinton famously defied the polls by defeating Barack Obama there in 2008, and Donald Trump did underperform his poll numbers somewhat when he lost Iowa.
Even though insiders now expect Trump and Sanders to triumph, their victories — if they do win — will still be major news. A year ago, the idea that a celebrity billionaire reality TV star and the Senate's only "democratic socialist" would be the two winners in New Hampshire would have been considered ridiculous. But these two outsider, insurgent challengers to the two parties have looked surprisingly strong for months now, and a New Hampshire win would give them justification for pressing on with their bids.
A Trump victory tonight would finally give the billionaire the win he's so craved and let him dominate headlines in the 11 days before the next GOP contest in South Carolina. And a Sanders first place would follow up his Iowa tie with a stinging defeat for Hillary Clinton, the Democratic frontrunner once considered the inevitable nominee. However, Sanders still has to prove he can improve his performance among the nonwhite voters who are so crucial to the party's coalition nationally — and he'd get an opportunity to do so in the Nevada and South Carolina Democratic contests later this month.
If Trump wins on the Republican side, another very important battle would play out for second place among that crowded field. Four establishment-friendly contenders — Marco Rubio, Jeb Bush, John Kasich, and Chris Christie — have all been within a few points of each other in state polls for months. Ted Cruz, fresh off his Iowa caucus win, is in the running for second place too. But expectations for Cruz are low in New Hampshire, since the state doesn't seem a great fit for an hard-right evangelical conservative. In the eyes of the political world, the real competition here is between Rubio, Bush, Kasich, and Christie.
Since Marco Rubio just won an unexpectedly strong third place in Iowa, he's been hoping a second place finish (or better!) in New Hampshire could cement him as the mainstream Republican alternative to Cruz and Trump, unite party elites behind him, and finally force many of his rivals out of the race. Indeed, a few weeks ago Rubio's team outlined their hopes that he'd finish third in Iowa, second in New Hampshire, and then first in South Carolina. After his Iowa finish, it was easy to see a Rubio versus Cruz versus Trump race taking shape. But then Rubio had a disastrous debate performance on Saturday, which has given his establishment-friendly rivals some hope.
Essentially, the worse Rubio does in New Hampshire, the more chaotic the GOP race will be in the coming weeks. If one or more of Bush, Kasich, or Christie manages to beat Rubio, whoever does so will likely stay in the race for some time and prevent serious consolidation of the party's mainstream around Rubio. The Florida senator will also be covered as a loser in the press, which will damage his prospects of doing well in South Carolina. Conversely, if Rubio beats all them despite his debate "glitch," he'll prove that his candidacy is durable and formidable, and likely lock up the GOP establishment pretty quickly afterward. Whether he can beat Trump and Cruz is another question.