if (DateTime . Now . Subtract(_lastRequestTime) . TotalSeconds < Config . instance . Field . WaitTime) {
    yield return new WaitForSeconds(1f);
    continue;
}

double nowTimeStamp = DateTimeExtensions . ToUnixTimeStamp(DateTime . Now);
if (ExpirationTimeStamp > 0) {
    float delaySecond = (float)(ExpirationTimeStamp - nowTimeStamp);
    delaySecond = (delaySecond < 0) ? 0 : delaySecond;
}