from typing import Optional


def get_image_provision_timestamp(log_path: str) -> Optional[str]:
    """
    Examines the Travis build log file at `log_path` to determine when the image used by the build was provisioned.
    :param log_path: The path to the Travis build log. This should be an original build log.
    :return: The image provision timestamp. None if the timestamp cannot be found.
    """
    with open(log_path) as f:
        for line in f:
            if 'Build image provisioning date and time' in line:
                # The next line is the timestamp.
                try:
                    return next(f).strip()
                except StopIteration:
                    return None