I think ten days is about right, but I would be tempted to divide the time equally. Look at the flight schedules to decide where to go first, in particular the choi e might be between arriving at SIN around 1am versus leaving SIN around 6 am. Try to time HKG arrivals and departures for when you can use the airport express train. If you decide to go to Macao,especially for an overnight, do it upon arrival by taking the hydrofoil or whatever directly from the airport, thus avoiding immigration and customs lines upon arrival at HKG.