Some institutions do it in one big "push" once a year; others stagger the reviews. As you have realized, it largely depends on the number of exemptions being managed and the staff available to do the work.
If you decide to stagger the reviews, adjust the review dates by doing some reviews earlier. To keep the example simple, if all your exemptions are next due for renewal in February 2012 (and it's currently August 2011), review 25% of them in November 2011, another 25% in August 2011. Complete the regular review for the remaining 50% in February 2012, and do half of those exemptions again in May 2012. In each case, plan to do the next review twelve months later. That sets up a quarterly review cycle, with 25% of the exemptions scheduled each quarter.
What you must not do is allow exemptions to go longer than 12 months between reviews.
John S. Burnett
Fighting for Compliance since 1976
Bankers' Threads User #8