Read the govt annual report on population to understand the race (not ethnic) quota. It's linked in this forum somewhere.
Secondly we think the approval system uses a gateway and sliding window throughout the year - it doesn't matter when you apply throughout the year - what matters is the macro view - i.e. are the General Election results driving PR approvals up or down (down at present) and are there race issues at play (yes - Indian and Other bucket is smaller).
Gateway is triggered for a set number of race based buckets at a set interval so your application goes into a race based pile which is refreshed at some interval (I don't think it's yearly but maybe quarterly and depends on the pop'n target which is reviewed regularly against birth and death numbers....) the approval window starts sliding... it's clear some ranking goes on within the race buckets and candidates are given high, medium or fail grades. The medium grades get pushed to the bottom of the pile and if the high-pot candidates dry up then they start digging into the medium graded applicants. I suspect the approval matrix and grading has a very fine granularity to it and some background checking built in (which can add delays for even high pot candidates) and possibly reports needed from the SIS etc.
In short I don't think it matters when you apply (in the year) but if you are a strong candidate and the wind is blowing in your favour from a macro point of view.
If you disagree with me consider the case of two singles, one a breeding age chinese malaysian woman of average education who applies in Sept and the older Indian of any gender with masters in say engineering who applies in Jan. The woman will get in almost straight away within the same year baring any negative issues in her background but the Indian fellow may never get in and if he does it could be up to 2 years.
The sorting in the pile is definitely not in order of application (within the window period) but by grading of suitability.