We've hacked the load order a bit to get t0 and mjd0 in _process_main().

def _process_hdu (self, hdu):
        "We've hacked the load order a bit to get t0 and mjd0 in _process_main()."

        if hdu.name == 'EVENTS':
            pass
        else:
            super (Events, self)._process_hdu (hdu)