Comparison of the number of bins in 500 s bin light curves and in optimal bin size light curves, colour-coded as in Fig. 4. In each panel, the top dashed line indicates the minimum allowed time bin of 5 s; the middle dashed line indicates sources for which the optimal bin size is exactly 500 s, and the bottom dashed line does the same for 5 ks. The number of bins for the 500 s bin light curve is an indication of the observation length, while lines parallel to the three lines already drawn indicate sources with a similar rate.