I'd have thought the spirit of the rules is so that you can spend time with a colleague waiting for a flight. Not really that you could guest someone in to wait 6 hours on their own for a flight when your own flight is already closing. The rules however don't specifically state this and are open to interpretation.

I have had the opposite happen (in Munich) where my flight was in 3 hours and the guests was in 1 hour and they still kicked up a fuss that it was a different flight.