FBB normally subjects players to a "cooling period" of 60 days after they have been signed as mid-season free agents before they can be traded. For our purposes, this is the same as 4 sims.
Currently, our league rules state that a player who is signed mid-season must be signed for one sim (approximately 15 days) before being traded.
Enacting this rule would mean that:
Players signed prior to the start of the regular season could be traded on December 15 (following Sim 3).
Players signed following Sim 1 (signing processed November 16) could be traded following Sim 5 (January 16, 62 days later).
Players signed following Sim 2 (signing processed December 1) could be traded following Sim 6 (Feb 1, 62 days later)
Players signed following Sim 3 (signing processed December 16) could be traded following Sim 7 (Feb 15, 60 days later)
Players signed following Sim 4 would not be eligible for trade that season.