Both F lounge opens at 5:30 so if you arrive well before that, the only lounge you could visit will be wing J.
Also the train at HKG will not operate after 6, it will be a long walk to Pier end. So I guess you might want to visit one of the Cabanas at Wing F at 5:30 sharp. There are only 5 of them and do fill up very quickly.
After you came out of cabana, you could take the train to Pier F for a proper breakfast.