So far, my wife and i are looking at 'caroline springs' (bout 20 mins) as it has lots of rentals available (newish looking ex display village I think).
Also against normal traffic enroute to tulla.
The only time the commute from Caroline Springs to the airport would take 20mins is at 3am.
Realistically, you'd want to allow at least 30mins for a 7am start, and up to 50mins for an 8 or 9am start.
You're certainly
not 'against' the traffic flow once you mix it with Melton Hwy & Calder Hwy traffic.
From Niddrie, Essendon North or Strathmore, it's a more consistent 25min commute depending on your proximity to the Freeway on ramps.