Ian uses this ability a lot of times, mostly when he is physically fighting someone. In "New Kid" Ian is able to dodge the blows his foe is lashing at him because he can see them coming with his ability a second before it happens. Other times though, the ability calls upon itself when it senses people nearby (Tunnel Man).
It is unknown if preflex can be controlled or called upon. It could be a possibility as Ian has not mastered his ability to its full potential.