What will be the minimum connection in HKG if I decide to clear immigration and take train to city, say Causeway bay area, assuming I have the BP for the next flight already? 5 hours?

I have TPE-HKG-SIN sector and now my HKG-SIN is only confirm on 01:15 flight. I am thinking to do some sight seeing in HKG before catching red eyes flight.

Any idea?