Thanks Whopity, that confirms what I thought about using the hour - it is valid. However, Lasors says
"If revalidating by flying experience, and providing
the examiner signs the Certificate of Revalidation
page within the 3 months prior to the rating expiry,
the validity of the revalidated rating will be calculated
from the date of expiry of the preceding rating."
My interpretation of this is that I'm better off waiting until there's 3 months to go before getting it signed by an Examiner.
Obviously letting it lapse creates a relative tidal wave of complexity, and I certainly shalln't let that happen! I don't want to diverge down the renewal/revalidate route, I understand the difference and will revalidate. What confuses me is the quote from Lasors above. I've met all the requirements now but that 3 months bit implies if I get it checked now it will run 24 months from now. It will only keep the original date if the examiner signs it with less than 3 months to go.