Projects on which the boss applied no schedule pressure whatsoever ("Just wake me up when you're done.") had the highest productivity of all. Of course, none of this proves that Parkinson's Law doesn't apply to development workers. But doesn't it make you wonder?
The decision to apply schedule pressure to a project needs to be made in much the same way you decide whether or not to punish your child: If your timing is impeccable so the justification is easily apparent, then it can help. If you do it all the time, it's just a sign that you've got troubles of your own.
Peopleware, pg. 29, Some Data from the University of New South Wales