When selecting by Delivery period, you create a selection and print the selected delivery period. The selection is then made per order row. Only those order rows whose delivery periods fall within the interval you enter under Delivery period will be included in the printout. By default, only the orders that have status 1-3 will be included in the printout.
When a delivery period is entered here, the form type alternative Order confirmation will be hidden, and another option will appear named Only not yet printed. If you print e.g. delivery schedule orders from here you can deselect this alternative/setting, when you want to print delivery notes for delivery schedule orders that have been partially delivered. In that case all order rows, whose delivery periods fall within the interval you enter under Delivery period, will be included in the printout. This applies to orders with status 1-5.