Seems an old system, Sydney too. I remember inbound to Syd early mornings from Sin. Some way out, ATC often said expect 20 mins holding at Parkes, I think it was.
I told them we could loose 10 min if we slowed to min cruise now to reduce the holding (better fuel outcome)
The reply normally was, even if we slowed down now the 20 min Holding would only start on arrival at the Hold point i.e. first come first served. Never understood the reasoning!