CAP371 (Yes UK) is what the HKG rules are based on I think and it differentiates between FDP and DP.
FDP is limited and DP determines your rest. There is no limit to DP in the FTL's, those limits are (normally!) specified in the rostering/employment agreements.
This is from memory, I have no references handy.
Further to this if you have a look at the link above you'll notice it is very similar to our FTL's just edited to remove a few inconveniences. I guess the total duty is limited to 55 hours so there is your px-ing limit!
(edited to add references)