Originally Posted by
LHR/MEL/Europe FF
I'm on the 0620 - so I was trying to get an idea of how busy the airport would be at the time of the morning (and the First class bit was just in case there were any priority queues etc which would speed up my progress).
First class bit doesn't help much until boarding, I'm afraid.
US CBP doesn't open until 5, but you can get into the queue before that.