You can be a Premium Silver member for much longer than a year!
Once you have met one of the two standards for qualification, your member category status will change automatically - it will not be necessary to wait under December 31 of that year.
For example: If, in the period between January and May, you have already earned enough kilometers or traveled enough segments to qualify for PREMIUM membership, you won't have to wait until April 1 of the following year (the official commencement date for the official Premium duration period) to begin receiving benefits. Once you have qualified, you will receive a temporary Premium membership card, which will expire on March 31 the following year. On that date, you will, receive you official membership card, which will be valid for a full year.