For setting up when a return window starts, simply log into your WeSupply account.
Go to Settings -> Returns -> Return Options section -> scroll down to the Return Window Start Date -> Select Order Date/Item Shipment Date/Item Delivery Date -> click on Save.
If you'd like, you can choose for the return window to start on the same day as the order was placed (Order Date). Also, WeSupply has access to the date when the order was shipped, and you can choose when the return window starts or when the order gets shipped (Item Shipment Date). Or, you can select the Item Delivery date if you'd like for the return window to start when the package is delivered to your customer.