The starting date would be the Due Date and the Offset would be -7 days (or -5 days if you include a 5-day Work Schedule). Remember to use Database Lookups in your conditions to make sure that the values are still the same for the criteria to be valid. When TR and CUR values are placed in the business rule, as variables they never change their value even if you schedule it far in the future. Therefore, you use DB Lookups so that at run-time the data will be re-evaluated.
Met vriendelijke groet,