In France it works the same as in the US or Brazil then in my experience, if the party is said to start at, say, 7pm it means that you can start showing up by that time but definitely not that you have to be here at 7 sharp. If it's a dinner I'd expect most people to arrive within the hour or so, if it's just some kind of party then I wouldn't be surprised to see people arriving a few hours "late". I would be quite surprised and probably not fully ready if I told a bunch of people to come to my party at 7 and they all showed up exactly on time.