Unfortunately I cannot give a time however it happens each weekend when the the frequencies are combined. Often caused by float planes north of Sydney on 124.55 I suggested to CASA that the 120.8 victor lane CTAF be extended to cover the Hawkesbury River. Got no where of course.
You only need one VFR self announcement on a departure frequency at the wrong time to cause problems. Does anyone know of any other country where VFR self announce on Departure frequencies of a big international airport? I bet not.