This functionality is designed for easier planning of crew that are not flying regularly on one specific aircraft as well as servicing the freelance crew.
When grouping crew by the aircraft in 3-dot filter it is possible to assign crew provisionally.
Right next to aircraft registration click 3 dots and click 'Assign temporary crew'.
In a pop-up window insert: Start of assigment, End of assigment and select crew member/members.
On the 'Crew Calendar' page, when the date range selected in the calendar covers dates of assignment (either start or end date), Leon will show crew assigned provisionally in italic.
Adding duties for crew assigned provisionally works in the same way as for regular crew.