def _get_time(header, keys, name):
        """
        Get time from header

        Args:
            header (dict): Object header.
            keys (tuple of str): Header keys.
            name (str): Method name.

        Returns:
            float: The number of seconds since the epoch
        """
        for key in keys:
            try:
                date_value = header.pop(key)
            except KeyError:
                continue
            try:
                # String to convert
                return to_timestamp(parse(date_value))
            except TypeError:
                # Already number
                return float(date_value)
        raise UnsupportedOperation(name)
Get time from header

        Args:
            header (dict): Object header.
            keys (tuple of str): Header keys.
            name (str): Method name.

        Returns:
            float: The number of seconds since the epoch