Legally, Camilla will be Queen Consort the moment that Charles becomes king, unless an act is passed preventing her from taking that title. Nevertheless, she will be called Her Royal Highness The Princess Consort.
Although she will legally be HM The Queen, she has stated that she will use the title and style of "HRH The Princess Consort", in a similar manner to her current use of the title and style of "HRH The Duchess of Cornwall" while legally entitled to use "HRH The Princess of Wales".
Of course, there is no certainty that Charles will ever become King of England.