Not a specific requirement as such, however it is somehow inferred here:
http://www.hkatc.gov.hk/HK_AIP/AIP/ENR/HK_ENR1.5.pdf
1.3 EXPECTED APPROACH TIME
1.3.1 If it is necessary to delay aircraft by means of radar vectors or holding, pilots will be advised of a further clearance time or an EAT only if the delay is planned to be for a period in excess of 15 minutes. If the delay is planned to be for a period of less than 15 minutes, pilots shall be advised 'no delay expected'.
As I think I explained on another thread earlier, as with most slot coordinated airports, the declared capacity and slot allocation mechanism necessarily results in inbuilt delay, with several flights often assigned exactly the same slot. In the case of HK, the schedule could be considered to be 'good' when the maximum delay to any particular aircraft does not exceed 15 mins, assuming the airport is operating at declared capacity.
You may be aware that HK ATC declares a tactical capacity at least twice per day,based on the actual forecast conditions (weather and operating criteria), and issues a notification message to all airlines and some neighbouring ATS Units.
If the delay is expected to exceed 15 minutes it is included in the message, and airlines are known to adjust their fuel policy for the day accordingly. CAD/ATC does not mandate the carriage of extra fuel in these circumstances- the onus is on the operators to determine their own policy.