Kaiten can show you which cards have been in one place for too long. Enable warning of stale cards 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 date after which the card will be considered stale.
Cards that are left in the column longer than the time you have specified will have a red card icon appear with the time the card has been left in the column.