Supposing you have a TAF3, arriving in Sydney. The TAF3 is from 220730Z and the conditions are fine to land ( no alt or holding required )

Then FM220900 the conditions change to 26006KT 9999 thunderstorms FEW015 BKN018CB

Your ETA is 0850Z

The question asked how much holding/alternate requirements are needed if the following is forecast at Sydney.

My thoughts that as long as you arrive before the FM, then no alternate or holding is required? Is this correct?

Assuming that if you were to land at 0900, then the conditions require that an alternate is required is that correct?

I understand that in the first 3 hours of TAF3, the time buffers do not apply, but will apply 30 minutes before and after if it is after the first 3 hours

I also understand, that in a TAF3, from ENR1.1  10.7.2.9 that only any reduction in visibility or if there was a PROB30 or PROB40 for TS or associated severe turbulence, then you can ignore this? But if there were other deteriorations ie. if the CLOUD was > SCT below 1500 at ETA, or if the wind was > aircraft could handle? or if there was a definate TS at arrival, then holding fuel would be required? Is this correct?

Is there any reason why CASA has included only 2 parameters to ignore and not the others 

Kind regards

Ravi