If you did not supply a license number when you installed your DBT, it runs in demo mode. Supplying your license here begins a 45-day period of normal operation even without activating your DBT. At the end of 45 days, you must activate DBT for it to continue normal operation.
Once you have entered your license, this option no longer appears. The 45 day trial period does not repeat.
Help: About DBT... displays the 45-day expiration date to help you keep track.