':return: The time (in minutes) between now and the call to start().'

def get_run_time(self):

    if (self._start_time_epoch is None):
        raise RuntimeError('Can    NOT    call    get_run_time    before    start().')
    now = time.time()
    diff = (now - self._start_time_epoch)
    run_time = (diff / 60)
    return run_time
