I don't think the Australian standard is about maintaining the arc - that's pretty easy, I think it's about "As I am approaching the arc, when can I call my self "established" and thus descend in accordance with the procedure?"
So, with a 90º intercept onto the arc, you would start the turn at 220 odd knots at about 1.3 miles or so - and may commence descent (as you are within 2 miles).