Dan Vasser has no control over when he travels through time. However, he usually has advance warning of when he is about to "travel": He develops a headache. When he feels a headache coming on, Dan quickly moves to a place where his sudden disappearance will not be noticed. When Dan returns from the past, he reappears at a point in time after his most recent disappearance. The amount of time that elapses between his departure and return varies from a few minutes to a few hours.