I think of party start times as guidelines. If it's a dinner party I'd like my guests there within half an hour after the start time. If it's just a 'bring a bottle' sort of party, any time is fine. But there's always someone who comes a few minutes early to mine. And I'm always still putting on lipstick, if not clothes.
But I have a friend who thinks that if a party starts at 7 (say), the correct time to get there is 6.50, with 7 being the latest possible correct time.
He's wrong, right?