This doesn't happen. People are just applying stereotypes to every possible context and situation. Germans are perfectly capable of coming to a BBQ later than the scheduled start time, although it's true that unless it's impossible for them to make their schedule fit with yours, if you tell them 5, then 5 it is.

Because of this, I would say it's even more important to schedule things sufficiently ahead of time. Making up plans only 2 or 3 days in advance, when weekend plans are mostly settled and they can't properly schedule around your event, will just stress people out.

> So how would it go in Germany?

1. the first one can occur, if they can't be on time they will ask if they can arrive later and as the host you get to decide whether they should still come or not, either way the guest will arrive on the pre-determined time

2. if the start time is flexible, this is stated clearly as part of the invitation e.g. you invite people for a bbq "starting around" 2PM (rather than at 2PM) and make it clear that they can arrive and leave at any point in the afternoon, just that they should not arrive before 2PM

A more interesting metric would be: You are meeting a buddy for dinner at some pizza place at 18:00. You are there punctual for whatever reasons, at what time would you ask yourself whether you would text your buddy? I think in Germany, the first text message might run 18:05 or 18:10 with lose ("I am sitting inside already") kind of a thing.

The haircut example would just mean you tell your friend in advance that you will arrive later.