3 months, and it's a revalidation if rating is still valid, renewal if rating has expired.
"Renew your rating
ATO assessment
To renew your rating, you must report to an approved training organisation (ATO) for an assessment to see whether you can undergo a proficiency check to renew the rating immediately or whether you will need to take refresher training first."
"Revalidate your rating
If your rating will expire within three months, you can apply directly to take a proficiency check at an ATO to have the rating revalidated, without having to take an assessment first."
Hope this helps!
CP