OLN has added a schedule page, breaking down the games by date and series, but no mention of any HD broadcast. If anyone knows about plans for OLN and HD in the playoffs, please feel free to post in the comments.
added 8:45pm, Just got the HD schedule for OLN-HD. Not sure yet if it will be on INHD or where, but I am sure information will be coming in soon.
April 22 - Game 1 Sabres vs. Flyers, 7:00 PM
April 24 - Game 2 Rangers vs. Devils, 7:00 PM
April 26 - Game 3 Devils vs. Rangers, 7:00 PM
April 28 - Game 4 Sabres vs. Flyers, 7:00 PM
April 30 - Game 5 Rangers vs. Devils, 6:00 PM
May 2 - Game 6 Devils vs. Rangers, 7:00 PM
May 4 - Game 7 Rangers vs. Devils, 7:00 PM