Set each booking to be specific time length

Hello.
Its possible in the Booking Calendar Business Small and higher versions.
Please read more about it here: https://wpbookingcalendar.com/overview/#range-days-selection
In these versions you can activate the “range days selection” mode and set minimum or fixed number of days selection as 3 days.
You can test it in action at the live demo (that configured by default for such type of days selection) here: https://bm.wpbookingcalendar.com/
Kind Regards.