If you are using AsiaMiles, have you considered using Dragonair to fly from KHH to HKG then CX on to SIN. That would, prima facie, be the fastest way to do it, and AsiaMiles awards allow CX + one other carrier for the same price as one carrier alone.

HAving said that - you get left with quite a long connection at HKG unless you are flying Tu,We,Th,Sa and could get the 08:20 departure from KHH, arriving 09:55, then 11:30 to SIN arriving 15:25. But that normally leaves you on regional business class, without the AVOD.

Having said that, despite my earlier advice, looking at the schedules I am reminded that there aren't many flights HKG-SIN with long-haul business class, so that might well be the best you could do. KHH-SIN in 7 hrs 5 mins. (Except, of course, taking the direct KHH-SIN flight on CI, which is 4hrs 5 mins, but that's not available in AsiaMiles.)