Check in opens when check in opens. I got there probably around 6-7ish (can't quite recall, but it wasn't as early as I had planned due to the awful awful traffic). Anyway, I had to hang around for 15 minutes before they came out and opened the desks. But some regulars I was chatting to said that they often opened as early as 4 in the afternoon.

Not sure about the lounge, I was the only person in there at around 8ish so I'm not sure what time it actualy first opens.