Best fit models of abundances vs. H₂ for CH₃ OH, C₂ H₅OH, CH₃ CHO, CH₃ OCHO, HC₃ N, CH₃ CN, CH₂ CHCN, and C₂ H₅CN using IC 5. G35.20 B1/B2 (top) is best fit by the fast model with a gas density of 10⁸ cm⁻³ over a time period of 1.3 kyr. G35.20 A (bottom) is also best fit by the fast model with a gas density of 10⁸ cm⁻³ over a time period of 6.4 kyr. The line colors for A are the same as B1/B2 as shown in the key. All species are shown in the key with color-coded dashed horizontal lines showing the observed abundances for the source. The thinner dashed lines indicate the upper limit and lower limit species that best constrain the time span. The time ranges in which all abundances can be reproduced within the errors reported in Appendix B are shaded. We truncate the x-axis scale to better highlight the chemistry changes over the temperature range at which the COMs are released from the ice mantles.