Upvote:5
For all sports events in general, the start time is the start of the final, official pre-game shenanigans which (depending on if it's the playoffs or something special) is close to the actual game start time.
They will often have up to an hour of other stuff beforehand - random awards, kids brought out to do something, remote control blimps dropping buffalo wing coupons on you, whatever. But as most pro sports are televised, the start time is effectively "when the cameras start rolling", which may involve a national anthem and coin flip or similar but that should only take 5-15 minutes under normal condition before the game itself commences.
Heh, you're apparently not the only high maintenance hockey watcher out there - here's an actual schedule from the Ottawa Senators indicating general buzzer time vs start time and surrounding times (note it depends on number of national anthems). It is apparently a NHL standard.