A bar countdown is used for to measure how much time is left in a bar.

To add a bar counter to a chart, right-click on the chart and select "Chart Settings" and select "Labels".

Find "Bar Countdown" on the "Available Labels" column, and press the > sign to add it to the chart. Press "Apply" and "OK". 

To edit the Bar Countdown, select the Bar Countdowns from the right list, and press the pencil "Edit" button.