You can commit to the program and become a registered Eco-School right away by applying for membership.
With regards to Bronze, Silver and Green Flag accreditation, every school is different, but a recommended approach is 1 level per year, for example Year 1 = register and work towards Bronze, Year 2 = Silver, Year 3 = Green Flag. Have a read of the Awards page for further information about this rationale and progression routes. Schools are also welcome to repeat a previously achieved level to build skills and confidence in a new cohort.
There are some Australian schools who are very advanced in their sustainability approaches and may wish to look immediately towards Silver or Green Flag Eco-School accreditation – please contact email@example.com to ask about this.