A dead time is a small period in the oscillation that totally cuts power to an output pin. I don't think this is needed, cuz i can't think of any reason you would want to do this.
A dead time is usually incorporated into Switch-mode power supplies, this stops both mosfets on the primary winding from firing on the same time.
If you did include the "dead time" the lo time would be extended, so if you had a 50/50 PWM this "dead time" period would alter the low time and aswell as the frequency.
Why do you need this dead time???