Converts epoch field to a float value (adding 24... prefix), or
        ``None`` if there is no epoch in GCVS record.

def parse_epoch(self, epoch_str):
        """
        Converts epoch field to a float value (adding 24... prefix), or
        ``None`` if there is no epoch in GCVS record.
        """
        epoch = epoch_str.translate(TRANSLATION_MAP)[:10].strip()
        return 2400000.0 + float(epoch) if epoch else None