The Lightning and whoever they play to start the 1st round of the NHL ploayoffs are going to play on Thursday, April 16th. It's not a question of how does anyone know this, it's who do we know this. No, that's not a typo, that's a reference to rock legends The Who. They (as well as Joan Jett and the Blackhearts) will perform at the Amalie on Wednesday night as part of their 50th anniversary tour.
If the game one is Thursday, game two is likely Saturday and game three on Monday at the opponent's arena. Schedule conflicts may lead to back-to-back games or an extra day off at any point of the schedule.