My concern as well for several reasons. Entry is not limited to a particular airline loyalty program, there will be a huge number of Amex Platinum cardholders visiting from the U.S., Centurion Lounges are generally noted for a better food offering than most lounges (at least in the US), and you can get free cocktails, so you may have to time your visit to guarantee access. Hours of operation were not announced but most Centurion lounges appear to be open from around 5 a.m. to 10 p.m.