When you set up Return Groups, you select how many days you'd like to give customers to return items. You should know how Returns Manager counts days and when they start and end.
For example, if you have a 15-day return policy, and a customer buys a product on the 1st of the month. No matter what time they buy the product, they have until 11:59 pm on the 15th to return their product, 15 days after their purchase.
When you create your return policy, take into consideration fulfillment and shipping times, and make it clear that your customers have until the end of the last day to make a return.
Note: Visit What are return reasons and statuses? for more information.