Hi You need to do cyclic DB scheduled rule. Then this rule triggers it launched the same db rule and so on. For example: Make Custom date field "Contol_Date"
Make in the template of SC this field to the current date (or make DB rule that will set control_date to current date after first saving of SC).
Make db rule: When service call is created OR When service call is modified where NOT (Control_Date (*) is empty) AND Assignment;To person is empty, Schedule the validation of this condition at 1 hour After Control_Date ff (Update Data) Control_date set to (Current date)
If this rule executes it will update control_date and so will launch the same DB rule. This will continue upon conditions will be satisfied.