Jabba-777:
I have no information about your Year 10-12 qualifications, you can either (1) email CAAS direct regarding this, or (2) you can email SIA HR for more information.
However, regarding your degree, it does not matter what results you obtain. SIA looks more for the O Levels or its equivalent. Check earlier posts for more infomation.
As for your flying experience, you should indicate your level of experience as you may get dispensation for the CPL/IR, just remember to indicate clearly what flights were those, ie, as PIC, any Cross Country flights...etc.
As for when is the best time to apply, there is no answer to that. So long as you fulfill the requirements like age, education, height, eyesight... you can apply anytime, and wait for the interviews / selections. Usually, there'll be a course that begins every month (approximately).
Hope this helps.