It is the scheduled arrival and departure time that matters for getting HK departure tax refunded.
You still had 8 hours in HKG so could have gone to try your luck...
If you want the connection to not be treated as a stopover, then morally I would think that your final destination is SIN and as you arrived on time, EU261 compensation should not be claimed
+1. It is the
scheduled arrival and departure times that are taken into account for the purpose of determining liability for HK Air Passenger Departure Tax (APDT).
The HK Civil Aviation Department's information sheet and form on APDT (
http://www.cad.gov.hk/english/pdf/DC...rmref=CAD-F038) state on page 2 that it is the "scheduled arrival time and scheduled departure time of the aircraft" that are taken into account when determining if you qualify for exemption.
If you look at the actual legislation (
Air Passenger Departure Tax Ordinance (Cap. 140)), Schedule 2 (page 6 of the pdf link) states that travellers who are exempt from APDT are:
2A. Passengers who-
(a) arrive at the airport from a place outside Hong Kong by an aircraft which, when the passenger ticket for the flight of the aircraft by which they so arrive at the airport was issued, has been scheduled to land at the airport on a particular day; and
(b) subsequently depart from Hong Kong by an aircraft which, when the passenger ticket for the flight of the aircraft by which they so depart from Hong Kong was issued, has been scheduled to take off at the airport on the same day as the particular day referred to in paragraph (a).
It would appear that, in your situation, you are not exempt from APDT.