PDF of the start time t_s (blue) of post-merger gravitational radiation to GW170817 following rejuvenation in gravitational collapse to a rotating black hole, setting the initial data to GRB170817A (top-left panel). The PDF shown (bin size 0.05 s) is superposed to estimates of the lifetime of the progenitor hypermassive neutron star formed in the immediate aftermath of the merger (reviewed in Murguia-Berthier et al. 2021). Highlighted is the 1.7 s gap (magenta) between merger time t_m = 1842.43 s and the onset of GRB170817A. Post-merger emission to GW170817 appears as a descending chirp in the (H1,L1)-spectrogram merged by frequency coincidences |f_H1 − f_L1| < 10 Hz (lower panels). For the merged spectrogram, parameter estimation (Fig. 4) derives from time-slides less than the duration τ of the templates (11) against a background generated by larger time-slides. Post-merger gravitational radiation is identified with the formation of the central engine of GRB170817A, whose duration is constrained by the lifetime of black hole spin (bottom panel).