It is now possible to automatically plan a day off after vacation.
Vacation is a duty type with the 'Vacation' checkbox ticked in the duty definition setup.
In order to schedule a day off after vacation, in the duty definition, you need to make sure that the 'Vacation' checkbox is ticked, and the 'Additional OFF' selected as per the screen on the right. 'Additional OFF' is a day off definition selected to follow the scheduled vacation period.
Once the definition is created, you can then schedule the vacation period either in the Crew Calendar or a Crew Timeline, and the additional day off will automatically be added, as per the definition (example below).