In this manuscript, we describe a simple and accurate method for finding the temporal overlap of the laser pump and electron probe pulse in ultrafast TEM. Our approach is based on the observation that the outline of a nanoparticle blurs at time zero, a phenomenon that arises from the PINEM effect. Aside from determining time zero, the blurring can also be used to characterize the instrument response, determine the laser polarization in situ, and map the near fields of nanoparticles, all without the help of an energy filter.