Thanks. That's a good question. I never thought to investigate that.
I've just taken a screen shot and times shown by CMS / Cameras 1,2,3,4 are
14:46:45 / 14:46:44 , 14:46:43 , 14:46:44 , 14:46:46 so the biggest error is 2 seconds. That's fine.
The CMS time is within 1 second of my radio...