That is up to your firm and your regulator. Remember that a critical aspect of the designation of a Specially Designated National (SDN) is that the SDN's assets must be frozen immediately, before they can be removed from U.S. jurisdiction. If a firm only scrubs its database quarterly, it could be 3 months too late in freezing targeted assets. Although the prohibitions and treatments for individuals and entities on OFAC's other sanctions lists are different from those on the SDN list, there may be similar consequences if your firm takes a long time in recognizing a sanctions list match.
OFAC's sanctions lists may be updated as frequently as a few times a week or as rarely as once in a month.