An American woman I know here was complaining that she invited some people for dinner at 7:30 p.m. and that at 8:30 p.m. they were just arriving. That is because in France, dinner is always (sauf exception) at 8:30 p.m., which means the guests will start to trickle in at 8:45. (If you are rude enough to arrive at 8:30, you will find your hostess flustered and possibly even still in the shower. This, by the way, proves that the American's friends knew they were invited at an earlier-than-usual time. They probably forgot exactly when and just retained "early" --thinking "eight.")
In France, there are times for things. The American management at Disneyland Paris, when it first opened (and was still called EuroDisney), was astounded to discover that everyone, everyone, stopped for lunch at exactly one o'clock. (And expected wine with the meal; but that's another story.) Dinner starts at eight-thirty, 20h30.... If someone invites you, you don't even need to ask. If tourists go to a French restaurant at 7 p.m., much less 6 p.m., they will discover the waiters and cooks eating.
This reminds me of the time I got sick and tired of how all French children's birthday parties (for lo, it is written) run from 3 to 6 p.m.... a horribly long time to keep a horde of small children amused. So I wrote on the invitation "15h à 16h30."
Of course, all the parents showed up at 6 p.m., except for the usual stragglers at 7.
