TV stations used a variety of on air clocks until the 80s when gaps in programming were closed, but you shouldn’t normally see the second clock (its a VT countdown clock). They are added to TV shows at the start of the content so the control room ops can fade the programmes in and out seamlessly, as it takes a few seconds for a analogue video recorder to get up to speed/synchronisation). They are still used today (there is still some lag in playing out a video stream) but often from 10 seconds only and sometimes with a peak white flash of one frame so automation can be set correctly. Their use still makes sense to identify what the following content actually is and that it has been edited rather than just being a rough collection of unedited camera footage.

(I must redo mine for 1080p which is a mission as you have to re-size 45 images, one for each second)

if that clock appears then someone has screwed up and/or the playout automation is kaputt…