The Act. Start Date is the actual start date of an operation set by the system when the operation is first updated with hours, quantity or a status. The “Date Worked” (from Job Status Updating) is used to assign this value.   In operation grid displays an "(R)" will appear next to the title to show you that it is a read only field.

If displaying the actual operation start date at the job header level, the term will appear as "Act. Op. Start" and shows the earliest actual operation start date for the job.