Distribution of onset times produced by the method for STEREO-A / SEPT 85–105 keV electrons from the SEP event of April 17, 2021. These are the same spacecraft, instrument, particle species, energy range, and event as in Fig. 3. The mean, median, and mode of the distribution are marked with vertical orange, red and blue lines, respectively. The red shading behind the histogram shows the times that bound ~68% of the distribution, and the blue shading bounds ~95% of the distribution.