Hot cores and their precursors contain an integrated record of the physics of the collapse process in the chemistry of the ices deposited during that collapse. In this paper, we present results from a new model of the chemistry near high-mass stars in which the desorption of each species in the ice mixture is described as indicated by new experimental results obtained under conditions similar to those in hot cores. Our models show that provided there is a monotonic increase in the temperature of the gas and dust surrounding the protostar, the changes in the chemical evolution of each species due to differential desorption are important. The species H2S, SO, SO2, OCS, H2CS, CS, NS, CH3OH, HCOOCH3, CH2CO, C2H5OH show a strong time dependence that may be a useful signature of time evolution in the warm-up phase as the star moves on to the main sequence. This preliminary study demonstrates the consequences of incorporating reliable temperature programmed desorption data into chemical models.