Wireless stations ( 108 - 1 - 108 -N) contending for exclusive access for a predetermined period of time (S 232 ) to transmit on a communication medium ( 112 ) are regulated by a common external controller ( 104 ) using a single timing parameter. Attempts at transmission access are preceded by respective delays (S 224 ) that are expired simultaneously and at a common rate by the stations at timeswhen the stations sense the medium to be idle. The delays are pseudo-randomly selected to avoid collisions (S 208 ) among stations in their respective access attempts. Default, initial values of the respective delays (S 204 ) applied to the stations, when multiplied by the respective expected number of transmission attempts by the stations over the long term over periods of time when no transmission attempt is unsuccessful, yield respective products equal to a constant value common to all stations (S 312 ). The default values therefore serve as a knob by which the controller regulates air time opportunity.