I report on a theory of time-dependent tunneling between a metal and a partially spin-polarized two-dimensional electron system (2DES). I find that the tunneling current which flows to screen an electric field between a metal and a 2DES is the sum of two exponential contributions whose relative weights depend on spin-dependent tunneling conductances, on quantum corrections to the electrostatic capacitance of the tunnel junction, and on the rate at which the 2DES spin polarization approaches equilibrium. For high mobility homogeneous 2DES's at filling factor $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$, I predict a ratio of fast and slow tunneling rates equal to $(2K+1{)}^{2}$ where $K$ is the number of reversed spins in the Skyrmion excitations.