I would say 30 mins for smooth traffic or 45 for traffic jam because 23 goes through busy streets in Causeway Bay and Wan Chai.
Another choice would be what rani suggested, which is to take the MTR to Central or Admiralty and catch a bus there.
You can:
1. Catch 4($5.3), 7($5.3), M49($5.0), 71($5.3), 91($5.3), or 94($5.3) at Heng Sing Back HQ along Westbound Connaught Road Central. 3A($5.3) is also available at this stop but during commute hours only.
2. Catch 46X($5.3) at Statue Square along Westbound Connaught Road Central.
3. Catch 3B($4.3) at Jardine House or City Hall along
Eastbound Connaught Road Central.
4. Catch 37A($4.7) or 90B($5.8) at Landmark along Westbound Des Voeux Central.
5. Catch 40M($5.3) at HSBC HQ along Westbound Queens Road Central.
6. Catch 23($5.7), 37A($4.7), 40($5.3) or 40M($5.3) at Pacific Place along Westbound Queensway in Admiralty.
Other bus lines are also available to HKU:
103, 970, 970X, or 973, which all come from Kowloon area.
HK's bus system is similar to NY's subway, which takes you all around the city in every corner...
