The relevant requirements are in
JAR-FCL 1.245(c)
You can meet all of the requirements (including the 1 hr with an instructor) within 12 months if you are re-validating by experience. It's only the proficiency check (if you choose to do it that way) that has to be done within 3 months.
Print out the relevant bit of JAR's above and show it to the examiner and he should sign you off.
(c) Single-pilot single-engine class ratings – Validity and Revalidation. Single-pilot single engine class ratings are valid for two years from the date of issue, or the date of expiry if revalidated within the validity period.
If therefore you revalidate by experience within 12 months of expiry your new rating will last for two years from the expiry date of your previous rating.
Mike