RingCentral Terminating PubNub SMS Subscription (PHP)

I tried and failed to find manual on RC PHP SDK. In my application I need to create pubnub subscription, send SMS and wait for the answer for 3 seconds, then terminate the subscription whether answer is received or not...

I tried

$subscription->setKeepPolling(false);

and

$subscription->remove();

but they all result in throwing an error. Is there a peaceful way to do this? And how can I create subscription for a limited period of time?

Thanks