All probes allocated by testRTC use an NTP server to synchronize their clocks. The server in use is Google’s NTP (more about it here: http://time.google.com/).
If you configure your servers to the same NTP servers, you will be able to synchronize the logs across testRTC and your infrastructure to the same timestamps.
Also note that all times in testRTC logs are using UTC timezone for the same reason. When showing the results in the UI, we convert the time to the browser’s timezone.