@Ken1979
If you go to your listing settings, choose 'availability' - you can then edit the ''check in and check out'' section.
Select ''Specify days of the week when guests can’t check out'' - here you can prevent Saturday check-out requests.
If you are absolutely content with only Thurs to Sunday people, you can fix the minimum and maximum trip length to 3 nights plus selecting 'Specify days of the week when guests can’t check in' and populating everything except Thursday.