If they were ever "requirements", that was a long time ago. The published holding details have always been "advisories" in the recent past. That said, things did change late last year.
Previously, the AIP text (ENR 1.1) was:
60.3.2 Standing advisories for traffic holding fuel for some major aerodromes are promulgated in ERSA. In other cases, when traffic delays for a particular aerodrome are anticipated,ATCwill advise the holding fuel by NOTAM. The pilot in command of an aircraft arriving at a destination without the notified traffic holding fuel will not be accorded a priority approach unless the pilot declares an emergency.
The AIP Revision of 13 Nov 14 (ENR 1.1) greatly expanded the text.
60.3.2 Standing advisories for traffic holding delays for Sydney, Brisbane, Melbourne and Perth aerodromes are promulgated in ERSA and are necessary to facilitate tactical flow management. Where delays are not expected to exceed these times no further advisories will be issued.
60.3.3 When traffic delays for these locations are expected to exceed these times, and in any case when significant traffic delays at other aerodromes are anticipated, ATC will advise the holding time by NOTAM.
60.3.4 Not relevant
60.3.5 All traffic holding advisories are estimates only and are based on the best information available. Actual holding may differ from the estimate, including to allow for effective traffic management. Operators should use their own judgement on fuel carriage decisions. Notwithstanding any advisories issued, the pilot in command of an aircraft arriving at a destination without sufficient fuel for actual traffic holding will not be accorded a priority approach unless the pilot declares an emergency.