https://operations.nfl.com/football-...ant-nfl-dates/
March 13 seems important...
MARCH 13
Prior to 4:00 p.m., New York time, clubs must exercise options for 2019 on all players who have option clauses in their 2018 contracts.
Prior to 4:00 p.m., New York time, clubs must submit qualifying offers to their Restricted Free Agents with expiring contracts to retain a Right of First Refusal/Compensation.
Prior to 4:00 p.m., New York time, clubs must submit a minimum salary tender to retain exclusive negotiating rights to their players with expiring 2018 contracts who have fewer than three accrued seasons of free agency credit.
Top 51 Rule begins. All clubs must be under the 2019 Salary Cap prior to 4:00 p.m., New York time.
All 2018 player contracts will expire at 4:00 p.m., New York time.
The 2019 league year and free agency period begin at 4:00 p.m., New York time.
The first day of the 2019 league year will end at 11:59:59 p.m., New York time, on March 13. Clubs will receive a personnel notice that will include all transactions submitted to the league office during the period between 4:00 p.m., New York time, and 11:59:59 p.m., New York time, on March 13.
Trading period for 2019 begins at 4:00 p.m., New York time, after expiration of all 2018 contracts