An explicit time-domain finite-difference technique to model zero-thickness space-time modu- lated Huygens’ metasurfaces based on the Generalized Sheet Transition Conditions (GSTCs) is proposed and numerically demonstrated. The equivalent Lorentzian electrical and magnetic surface susceptibilities of a typical all-dielectric Huygens’ unit cell, χee and χmm respectively, are mapped for a range of material permittivites, which is modulated in both space and time. The problem is formulated using a set of second-order differential equations in time with non-constant coefficients. The field solutions are then solved using an explicit finite- difference time-domain technique and propagated both in the time domain and the frequency domain. Several examples of a metasurface with static or space-time modulation are shown for normally incident plane and Gaussian beams, showing the scattered field solutions. While the time-modulated metasurface generated new colinearly propagating temporal harmonics, the introduction of a space-time modulation caused the generated harmonics to travel with differing angles of refraction.