1:05 should be plenty of time. You just go through the transfer desk without going through immigration or customs. It's all airside so you won't need a visa. CX might mistakenly give you a hassle in HKG, but if you're worried just apply and get a VoA letter. It's very cheap. (Not recommending it, but some of the travel agents sometimes produce "proforma" letters to get you by the airlines and then exchange it for a real letter when you arrive SGN before you go to the visa counter. )