i've found out there's no point of following the operating hours, basically they open for bigger international airline. e.g if you are taking singapore airlines, they will 100% open, if there's only jetstar, they won't open.
just checked my upcoming flight with singapore airline, 4 business class, departure time is 6:35pm
it means there's no international lounge for us to go...what a joke, a lounge that only opens 3.5hours in the morning.