def METHOD_NAME(self):
    """Writes the current (UNIX) time to the file.
    Times are stored as a list in the file's ``attrs``, with name
    ``run_start_time``. If the attrbute already exists, the current time
    is appended. Otherwise, the attribute will be created and time added.
    """
    attrname = "run_start_time"
    try:
        times = self.attrs[attrname].tolist()
    except KeyError:
        times = []
    times.append(time.time())
    self.attrs[attrname] = times