T(-) Countdown Control already has the ability to store a visitors calculated launch time to a cookie. As of version 1.7.7 we have added integration of a new add-on plugin T(-) Countdown Tracking. This new premium plugin adds the ability to save the visitors IP address in the database. More details to follow.
Test using Schedule:
Counting Down to Mon, 1st May, 2017
Test using basic shortcode:
[tminus t="+2 minutes" id="test_counter" track_id="2571" /]