They have a timeout, the clock stops on any incomplete pass, and you don't want NE to have time to score *if* you get a TD.
It's probably a good call on 2nd down by Seattle from a time/game management perspective - run the clock down under 30 seconds when the Pats let you, and call a pass play. That way, the clock stops on any incomplete and you have 2 Marshawn shots from there. Pats just hit their 1-outer on the step-in-front/RW not reading such.
Your only time issue after running the clock under 30 seconds (from Seattle's perspective) is really if there's an automatic 1st down penalty (defensive holding, PI, etc.) and you all of a sudden have 4 downs again.
<<<<Or something, still confused.