Afraid I am acquainted with fewer than ten hotel lounges, and my fave is Conrad Singapore. Open 0600 till 2300, great staff (including one young lady who ever so deferentially and apologetically reminded the four of us guzzling sparkling wine of the published closing time - at about 2325). We felt quite guilty and finished up right away! And in theory (I did
not try this

), while the drinks are only out on display during arvo tea and the hors d'oeuvres session, you can order one at any time, so in fact could spend 17 straight hours drinking every day (plus any 'bonus' late closing), if that was your desire. Drinks are decent (sparkling, not champagne, but good enough for my tastes) and food for arvo and evening sessions is plentiful and varied. I don't think I ever ate breakfast in there.