Today is the de facto deadline for trades involving players who have cleared waivers.
I believe you can technically make deals up until season's end, but since a player who isn't on a team's roster today isn't eligible for post-season play (yeah, that is an oversimplification, but it is applicable here), for all intents and purposes, a playoff contender wanting to add a piece is going to do it today or not at all.
There have been some very quiet rumblings about the Rangers possibly being willing to make a move today, so it is worth keeping your eye on...