Renewing your membership will extend it 12 months from your current expiration date so no time is lost.
The clubs get rated by the business they do. This is one reason I always try to check into the club when arriving at an airport and not just when departing. They also get credit for any membership transactions, so if you do have a reason to be in your club before your current membership expires (or shortly thereafter), then I suggest holding off and let them take care of it for you.