If the Intro Timer (countdown timer) has disappeared, it's likely that you either disabled it deliberately or that you may have unintentionally clicked on the close button ( [X] ) of the panel containing the Intro Timer.
To make the Intro Timer visible again, use the main menu item View and make sure the item Intro Timer is checked, as shown here.
Intro Timer Enabled
See the topic on Using the Intro Timer for additional details on enabling, disabling, and using the countdown timer.
