A method for constructing delay rules which include the effects of MIS simulations for static timing analysis with reduced cost. The present method includes constructing skew windows for applying MIS penalties purely from SIS data, and scales the MIS penalties during rule use based upon how closely the skews in the use case approach the edge of the skew window. The method applies both to timing rule construction for a library of circuits and to timing rule construction for macros where only part of the circuits in the macro may be sensitive to skew between macro inputs.