Bookworm is right, it can be signed any time in the last 12 months.
So in theory if on the first day of the second 12 months you fly 12 hours ( inc 1 with an instructor) you can get your sep revalidated for 3 years
Does it need to be an examiner that signs the renewal? I know someone signing away who is an FIC and that does not seem to cause problems. The only time an examiner needs to get involved if if you lapse the SEP.