These dates appear to be (mostly) official:
Roster deadline: Dec. 24, 6 p.m. (15-player roster limit)
Trade deadline: As of now, March 15 (Target date)
Guarantee date: All contracts become guaranteed Feb. 10.
Start of 10-day contracts: Feb. 6.
Active-roster reduction: Feb. 6. (12 active players)
Rookie-scale extension deadline: Jan. 25.
Playoff-eligibility: This deadline has yet to be established.