The league will not make any official schedule announcements for the Playoffs until Wednesday 4-16. They may have to wait until that night's games are complete to determine the matchups. The schedule may be released so late that it's effectively Thursday 4-17 by the time it's announced.
If the Bruins win tomorrow (Tue 4-15), then they will DEFINITELY host the Canadiens on Saturday, 4-19. If they win tomorrow, the NHL will most likely announce the Saturday game time, by noon on Wednesday 4-16. The Bruins cannot be eliminated from the playoffs before Thursday night, after the NBA schedules have been set for the weekend.
If the Briuns play on Saturday afternoon, the Celtics may play on Saturday evening. My worst-case scenario--I have to play a gig in Somerville that night. We don't play until about 10:30 or 11:00 pm, so I'm hoping for an early start time and a Celtics blowout, and I'll leave the game early. It's possible for the Celtics to play the matinee, and the Bruins play in the evening, but hockey after basketball at the Garden is quite rare; not nearly as common as basketball after hockey. It's also possible that the Celtics will play on Sunday. The NBA always schedules every playoff team to play on Saturday or Sunday of the opening weekend of the Playoffs, and I don't see any reason to expect that to change.
The TV crews, the Garden staff and management, the leagues, and the teams, may have advance information, but it may be subject to last-minute changes as the NBA season comes to a close and the NHL playoffs progress. The NBA really needs to know the results of Wednesday night's NBA and NHL games before the make anything final. So, even if you have a little Larry Bird with secret information, the information may change.
I'm hoping for a Sunday game. If Atlanta win 1 more game, or Indiana loses 1, we draw Atlanta and Indiana is out. If Atlanta loses 2 and Indiana wins 2, I believe that means we draw Indiana and Atlanta is out.