def _values_valid(d):
    """
   -> boolean: True - valid duration
   -> boolean: False - invalid duration
   """
    m, s = d
    if m is None and s is None:
        return False
    if m is not None and s is not None:
        if m == 0 and s == 0 or s >= 60:
            return False
    elif s is None:
        if m == 0:
            return False
    elif m is None:
        if s == 0:
            return False
    return True
