If you encounter the "WebRTC Connection Timed Out" error, please do the following:
1) Try clicking the "try again" button on that same page. This may permit the connection to be established.
2) But if the error persists, it's likely caused by a latency (delay) on your computer and/or network. The best thing for you to do is to exit LockDown Browser and restart your computer. After the restart, be sure to shut down all other running applications on both the computer and the network. If using WiFi, move as close to the router as possible.
3) Then start up LockDown Browser and try again.
4) If the problem persists, try using a different network, or a hardwired connection via an Ethernet cable.