Apologies for bringing up an old topic, but just want to point out to anyone else who finds this thread that this syntax:
myTimeline.tweenTo("zoom1").duration(3);
Doesn't work - the tween continues at the previous duration, even though the duration property reports back the changed value. You have to manually do it as was posted above:
timeline.pause();
TweenMax.to(timeline, 2, {time:timeline.getLabelTime("zoom1"),ease:Quart.easeOut});