FlowFast can show you which cards have been in one place for too long. Setting a card's expiry date can help you pay attention to such cards, find hidden blockages or review the relevance of a task.
Click the three dots next to the column name. From the drop-down menu, select "Enable warning of stale cards"
In the window that appears, select the period of time after which a card will be considered stale.
Cards that are in the column longer than the time period you set will have a red icon indicating the period of time the card was in the column.