When you plan crew roster in a plan mode, apart from selecting to whom plan should be published, you can also select start & end date.
Once it's published and you're back to actual mode you can define the end date of the published roster by using a link Roster efective date whi you can find right below the month (top-left corner).
If it's not set it shows as 'Roster efective date is not set (set)' with the active link set. Click it and select the proper date and Leon will show a blue line across the screen. That is the published roster end date.
If you have any planned duties (but not published yet), Leon shows them right behind the line in the 'Plan Mode'.
You can always change that date - Leon shows the link as 'Roster efective date is DD-MM-YYYY (change)'.