Actually its the oppossit. Well, to my feel :)

Heavier picks dont bend that much. So when you do fast picking, the pick responds better timing wise. A lighter pick will bend a little and will affect the timing of your picking hand and the fretting hand.
Where talking about quarter of seconds probably but that can be a lot if you are really fast :).
But thats something you can get used too by timing your left hand with the right hand accordingly. So it always comes down to what you feel is better for you :)