There is no time limit on a takeoff alternate in oz - unless your company mandates it. You just have to get somewhere else in any timeframe (less than max endurance!). Most other sensible states follow ICAO Annex 6 stating a 60 minute takeoff alternate if dept weather is cr@p.
If an EDTO airport went out in cruise - and you were already past your EEP, what states you have to divert to remain within three hours of another EDTO alternate? Why couldn't you just keep going?
And your EDTO area is predetermined by distance - not time. This is a common misconception. It is the distance travelled in a time (eg 180mins) at a predetermined speed and weight. For arguments sake, let's assume your EDTO threshold is 1300nm @ 180 mins. You can now fly up to 1300nm from your nominated EDTO aerodrome, irrespective of winds. If then you had a 100kt headwind for the divert, you'd end up taking 234 mins to get there. Totally legal under the regulations. Of course your EDTO xtra fuel on your plan would be significant.