In this study, the effect of the adsorption contact time (ACT) on the desorption characteristics of coking coal particles is investigated using mercury intrusion, N2 adsorption/desorption, and methane adsorption equilibrium/desorption tests. The results of these tests reveal that the presence of micropores with one side closed, which we call half-open pores, in coal particles is the main factor affecting the duration of the equilibrium process. Coal particles subjected to different ACTs exhibit different adsorption contents, which strongly influences the desorption characteristics. The higher the ACT, the greater the volume being desorbed and the more durable it is. Considering that the adsorption content is equal to the limit of the desorption content, a new mathematical model of desorption under different ACTs is proposed, and the model output agrees well with the desorption curves. Using the diffusion coefficients fitted by this model, the adsorption equilibration period can be estimated, which will be useful for engineering applications.