I visit all three cities regularly for business, but I rarely use taxis, as the metro systems are so good. I don't know why you would want to hire a taxi by the hour, it's always faster and cheaper to take a train then if necessary take a taxi for the last mile.
In Singapore last week, there were three of us with luggage so we took a taxi from the airport to the city center, about 30 minutes, for SGD 28 (metro is SGD 3.5). A typical ride of 15 minutes in light traffic was around SGD 10-15 (metro for the same distance SGD 1.5). I often make a day there, landing around 0900, taking 4-5 meetings around the city, then departing around 1700 without ever needing a taxi
In Tokyo, don't even think about a taxi from the airport, they are extortionate at about JPY 30,000 compared to a "limousine bus" which is about JPY 3500 or the JR Narita Express train which is about JPY 2000. Around the city a 15 minute ride in moderate traffic is about JPY 1500 - 2000.
I've never taken a taxi in Hong Kong, all my needs are in the city center and easily serviced by metro. The express train from the airport is about HKD 120 if I remember right.