The deadline is usually July 15th. But because the 15th falls on a Sunday, the deadline for a franchise player to reach a long-term deal this year is EOB, July 16th.
http://www.nfl.com/freeagency
As a franchise player Samuel has until November 13th to sign his tender in order to play during the 2007 season.
Q -- What is the time period for free-agency signings this year? A -- For restricted free agents, from March 2 to April 20; for unrestricted free agents, from March 2 to July 22 (or the first scheduled day of the first NFL training camp, whichever is later); and for franchise players, from March 2 through the 10th week of the season (Nov. 13).
http://www.nfl.com/freeagency/qa
From the CBA itself:
"If a Franchise Player (Samuel in this case) does not play in the NFL in a League Year, his Prior Team (the Patriots) shall have the right to designate such player as a Franchise Player or a Transition Player the following League Year, if such designation is otherwise available to the Team, except that the applicable tender must be made and any 120% tender shall be measured from the Player’s prior year salary. If such a player is redesignated as a Franchise
Player for the League Year following the League Year in which he does not play, the player may be designated only under Section 2(a)(i) above, except that Draft Choice Compensation of only one first round draft selection
and one third round draft selection shall be made with respect to such player in the event he signs with the New Club. If such a player is designated as a Franchise Player for a third time, the terms of Section 2(b) above, shall
apply. If a Franchise Player who has sufficient Accrued Seasons to become an Unrestricted Free Agent is not designated as a Franchise Player or Transition Player for any League Year immediately following a League
Year in which he does not play, then on the first day of that League Year, the player becomes an Unrestricted
Free Agent and is completely free to negotiate and sign a Player Contract with any Club, and any Club is completely free to negotiate and sign a Player Contract with such player, without penalty or restriction, including, but not limited to, Draft Choice Compensation between Clubs or First Refusal Rights of any kind, or any signing period.