Tuesday, October 14th is the absentee ballot request deadline. For those committed presidential organizers planning on running up to New Hampshire for get out the vote efforts come November 4th, you will need to turn in your ballot request (and it cannot just be postmarked by the 14th; you will need to deliver it to your Board of Canvassers in person).
Here is the application PDF.
Here is a list of Boards of Canvassers. Call them if you have any questions about the deadline.