Even as the two presidential candidates fly from one battleground state to another and as the cascade of campaign ads rolls over television viewers, some fast-approaching deadlines are going to determine who will in fact get to vote on Nov. 6.

The National Association of Secretaries of State has declared September National Voter Registration Month and Sept. 25 as National Voter Registration Day. In 48 states voter registration deadlines fall in October.

One imminent deadline is this Saturday, Sept. 22, the date – 45 days before the general election – which is set by two federal laws, the Uniformed Overseas Absentee Voting Act and the Military and Overseas Voter Empowerment Act, for election officials to send ballots to voters in the military and to civilian voters living outside the United States.

“There needs to be time for the ballot to get to the voter and back by Election Day – and that means 45 days” before Election Day, said Samuel Wright, director of the Service Members Law Center in Washington.

Americans in the military who are serving around the world are eligible to vote “but the problem has always been getting them their absentee ballots in time so that they can mark those ballots and send them back in time to be counted,” Wright said.

Kevin Lamarque / Reuters

President Barack Obama, Jorge Ramos and Maria Elena Salinas take part in a town hall hosted by Univision at the University of Miami in Coral Gables, Florida September 20, 2012.

In 48 states (other than Alaska and Maine) absentee voting is administered by county officials, or by city, town or township officials.

Wright said that some of these officials are responsible for small rural areas, “but the military are over-represented from small towns and rural areas. So even if you’ve only got three servicemembers from some small town in northern Wisconsin, they need to able to vote and it’s up to the local election official to get the ballot out in time.”

In past elections, some local officials have been late in mailing ballots to overseas and military voters. “Congress finally got tired of waiting on the states to fix this problem and in 2009 Congress added an explicit requirement: 45 days.”

Here are other looming deadlines that may determine who gets to vote:

• Tuesday, Oct. 2: This is the date by which Pennsylvania state judge Robert Simpson has been ordered by his state’s Supreme Court to issue a ruling on whether state officials will be able to provide identification cards to voters who might be deprived of the right to vote by the voter ID law signed last March by Republican Gov. Tom Corbett.

In its ruling on Tuesday, the Pennsylvania Supreme Court said that Simpson needed to assess the procedures officials are using to ensure would-be voters who don’t have driver’s licenses will be able to get the alternative state-issued ID cards.

But Simpson’s ruling on or before Oct. 2 could be appealed to the state Supreme Court, which might push a final resolution of the dispute very close to Election Day itself.

“The closer we get to the election, the greater the danger of confusion,” said election law expert Prof. Richard Hasen at the University of California, Irvine, the author of the new book, The Voting Wars. “The (United States) Supreme Court in Purcell v. Gonzalez (a 2006 decision) warned courts against changing election rules in the days before the election, which is what made the recent Pennsylvania Supreme Court decision so puzzling: it will push the decision on voter ID almost up to Election Day.”

He added, “No matter what the courts ultimately decide in Pennsylvania, inevitably there will be confusion at the polls, with some thinking  ID is required and others thinking it is not -- and both being reasonable thoughts given what's been going on.”

Oct. 2 is also the day on which in-person early voting begins in Ohio – although it is not yet finally settled when the early voting period in that state will end. The state has filed an appeal to a ruling by a federal judge that would allow early voting to continue until Sunday, Nov. 5.  The Obama campaign had sued the state after the legislature limited in-person early voting hours for most voters except military voters.

• Saturday, Oct. 6: This is the earliest deadline for registering to vote in any state. It’s the deadline in both Mississippi and in Nevada. The latter state is especially important since it has a crucial Senate race (with Republican Sen. Dean Heller facing Democratic challenger Rep. Shelley Berkley) and is competitive in the presidential race.

• Tuesday, Oct. 9: This is the deadline for registering to vote in 13 states, including the hotly contested ones of Ohio, Florida and Colorado.

• Monday, Oct. 15: The deadline for registering to vote in Virginia, which some analysts see as a must-win state for Republican presidential candidate Mitt Romney.

• Tuesday Oct. 30: This is the deadline for requesting an absentee mail ballot in the battleground state of Virginia. But absentee ballot request deadlines vary by state. Also some states, such as Virginia, require a reason for voting by absentee ballot while others, such as California, do not.

• Sunday, Nov. 3: The in-person early voting period ends in the battleground state of Florida. But Democrats have filed a federal lawsuit challenging the decision by the Florida legislature to set the early voting period at eight days (rather than 14 as the law previously did), or a total of 96 hours. A federal judge heard arguments in that case Wednesday and is likely to issue a ruling soon.