When NBC shows hockey on Sunday, their time slot is usually 3pm eastern. It's been that way all season. At least that game won't be on NBCSN.
As for why the games won't start until Sunday, 2 reasons. If it starts Friday, a 4 game sweep (not likely) gives NBC only one weekend game. Starting Sunday guarantees 2 weekend games for each series. NBA does this all the time. More sports are watched on the weekends than weeknights. And the NHL isn't big like College Football or NFL. They can't compete with prime time television on a major network (NBC).