Hello, I am not a frequent flyer and I will be in Copenhagen after a cruise. I will stay in Copenhagen for a few days after the cruise and I have an early morning flight (6:40 am) out of Copenhagen that will connect in Frankfurt to San Francisco, Co. What time do I need to be at the airport? Normally for an international flight it's 3 hours but I wonder if the check-in for Lufthansa will be open at 3:30 am on a Sunday.