We have measured and simulated dynamics of magnetization reversal in a micrometer scale Ni80Fe20 polycrystalline thin film element in the time domain. The sample is probed experimentally using time-resolved scanning Kerr microscopy. This allows for spatially resolved images of the dynamical magnetization states. We have simulated these magnetic reversals micromagnetically for the case of an ideal rectangular element. The reversal rates agree semiqualitatively, and gross spatial features such as a stripe instability in the directions perpendicular to the applied field are reproduced. © 2000 American Institute of Physics.