85–105 keV electron intensity as observed by STEREO-A / SEPT during the widespread SEP event of April 17, 2021, averaged to a time resolution of 3 min. With 1000 bootstrap runs, each of which used a random sample size of 35% of the data inside the background, the method found a number of possible unique onset times that are displayed on the right of the figure with their respective distribution shares. The background window was set to 08:00–16:00 and is highlighted in light red. The most probable onset time (19:14:33) is marked with a vertical solid red line, while the rest of the onset times are marked with dashed lines. The depth of the color-shading indicates their relative popularity.