Returns the most recently added child tween/timeline/callback regardless of its position in the timeline.
var tl = new TimelineLite();
tl.to(e1, 999, {x:100, repeat:5}) //very long tween
.to(e2, 1, {y:200}, 0.5); //insert this tween at 0.5 seconds (toward the beginning of the timeline)
.to(e3, 1, {scaleX:2}, tl.recent().endTime() + 3);//inserts the new tween 3 seconds after the e2 tween which was added most recently.