Yes, the arrivals lounge in the Sofitel will be open to welcome guests from the first BGI flight. And being the first flight of the day you'll practically have the place to yourself. Last time I checked it out was in November last here and though the flight over from BGI was packed as usual both in CW and in First, I was the only person using the lounge. It's a loooong way from arrivals so I guess most people would rather give it a miss. By the looks of it not many of my co-travellers were heading to work the next day anyway. At any rate, staff very friendly and the lounge a pleasant experience.