A modeling method to incorporate transparency into black box models using setup time in a circuit timing model. The circuit timing model, comprising a plurality of latches initially represented using black box models, is generated. For each of the plurality of latches, an arrival time is calculated from the latch clock pin to an interface data output pin of the timing model, and the maximum arrival time is determined. For each of the plurality of latches, a setup time is calculated. A setup time is also calculated using the delay time from the interface data input pin to the interface data output pin and the maximum arrival time. The worst-case set up time is selected from these setup times and imposed at the interface data input pin. Satisfaction of the worst-case setup time causes the maximum arrival time to also be satisfied. Therefore, a transparent path through the latches in a black box timing model cannot generate an arrival time at the interface data output pin greater than the maximum permissible arrival time. Thus, the timing constraints used in the black box timing model are not unnecessarily restrictive.