Exactly what it says.....
I know on Concorde you can arrive I think 30 or 20minutes before departure, very handy for businessman, celebrities and the like.
Personally, I prefer to check in about 2hrs before departure, gives me time to browse the Duty Free for a short time and enjoy a glass of champagne or a pint in the lounge an relax
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'There are only two emotions in a plane: boredom and terror'
Orson Welles (1915–1985)