If you revalidate the rating while it is still in date, it will be a proficiency check. Generally examiners make this last an hour, as any less will have the CAA asking questions on whether everything was covered. Generally it doesn't involve much of a nav section, just general handling based stuff and circuits.
If you let it expire, then it will be a full retest, including the nav section, which could last anything from 1:30 to just over two hours.