Though I would give at least two minutes when the traffic is being relayed through Flightwatch on HF.
This is the only time we (you) NEED notice. A lot of these rules were written for Flight Service, in the days when a significant proportion of comms were on HF, even in the cruise, and nobody wanted to call aircraft in case they didn't answer, which could up the workload remarkably. If I was sitting in Perth and heard a call to Kalgoorlie (that Kalgoorlie didn't) the notice would give me time to call him & get a traffic statement and call you back.
I don't need notice on VHF, I've probably already passed any traffic I consider to be immediately vital. I regularly see on my radar screen the Mode C readout going 150, 150, 149, 148, 146, "Senna, ABC, request traffic (grinding of teeth) for descent Urblegurble."
I suppose there are also times when coord to another controller is required to give them the opportunity to assess traffic also.