I think it really depends on the departing Immigration queue, which can vary.
Check-in with Star Gold should be quite quick.
Airlines have different time schedules for when the last check-in is allowed, and when gates close.
I think you will be required to show a paper boarding pass, at security, for departing Immigration and the reader at the gate.
And can you drill down on your question a bit. Are you asking what is the minimum time before scheduled departure that you can arrive where? Curb, counter, gate? Or do you want us to factor in travel time to the airport from some unknown location, via some unknown means?
Personally, I wouldn't arrive much later than say 90 minutes prior to scheduled international departure. On a recent trip to Hong Kong, the immigration queue departing was quite lengthy, ~ 40 minutes.