def container_convergence(results, limit):
    """
    Calculate the percentage of containers that converge within a given
    time period.

    :param results: Results to extract values from.
    :param limit: Time limit for container convergence in seconds.
    """
    convergence_results = [
        r for r in results if r['metric']['type'] == 'wallclock' and
        r['operation']['type'] == 'create-container'
    ]
    num_convergences = len(convergence_results)
    if num_convergences > 0:
        convergences_within_limit = [
            r for r in convergence_results if r['value'] <= limit
        ]
        return float(len(convergences_within_limit)) / num_convergences

    return None