It is to divide overhead by number of Jobs worked, not hours.  If the OH rate in the work center is $45/hour and the employee is simultaneously clocked into 3 jobs then if you answer Y to the SD-Q prompt, each job will be charged $15/hour.   Standard DBA will charge each job $45.  There is a SD-B setting in standard DBA to divide Labor by the number of jobs worked but Overhead never had that option.