In an easy way you need to create a parameter and a calc field to help you with this.
Parameter will carry the date values. Lets say the parameter is [DateSelected], now create a new calc field [DateInRange?] which will be DATEDIFF('day',[YourDateColumn],[DateSelectd])<=12. This calc will return a bolean answer TRUE or FALSE, put this calc field in filters and select true this will help you get the desired results. If you still have some questions please share a .twbx workbook, it'll help us understand the issue in a better way.
Thank you very much for your help. Another great function I will have under my utility belt. Thanks!