This column appears if the setting Use queue time exceptions on operations? has been configured under the heading Preparation that you will find under the Manufacturing tab in the Settings procedure.
If so, you can enter a queue time in number of days for the operation. The queue time that is entered for an operation row here will override the queue time entered for the work center in the Update Work Center procedure. In the Queue time work center column you will see the default queue time on the work center.
During order replanning, the system will also take this queue time exception into consideration. The default is to leave this column empty, and then the queue time will be loaded from the work center.