This is a configurable setting your credit union can choose, and there are actually two separate default purge periods you can specify: one for stop pay orders created in CU*BASE (by a CU employee) and a separate period for stop pay orders created by members via online banking.  The CU*BASE default is typically set to 6 months, and most credit unions set the online banking default to 14 days (because of the way regulations specify that if the order was oral and not confirmed in writing then it lapses after 14 days).  But you can set either one to a different period if you wish.  In addition, you can control the purge date on a stop pay order by changing the date on that particular record.

For online CUs, if you want to change either setting, contact a Client Service Representative.  For self processors, the CU*BASE setting is controlled via OPER > 10 > 1 Master CU Parameters (screen 5) and the online banking setting is controlled via OPER > 10 > 8 ARU/Online Banking Configuration.