Agent Heartbeat

I was wondering if anyone knows how to change the heartbeat of the agent to the server. I have agents that I know are offline and have been offline for over an hour and yet in the agent console it still shows that they are connected. I would like to change the heartbeat to 15 minutes. Yes I know it will create more chatter on the network. But we need more accurate reporting.

I did search and found one article but the answer is not clear. Not sure if just changing ServerCommunication.CONNECTION_INTERVAL_SECONDS.int to 1800 seconds will do the trick.

Does anyone know for sure if this will work?

Thanks