Are you sure about that? As mentioned earlier, if programmes went past midnight on a Friday or a Sunday then the company continued.
Unless that was the official timing but they just ignored it when it happened?
In the late 1980s or early 1990s, there was a situation where a film began during Thames broadcasting hours one Friday, and finished during LWT's time, and I believe the changeover happened during the film. I'm sure the video is on youtube of the ad breaks, and the description of the video makes mention of that.
Yes that happened occasionally and regularly with Home and Away in the last year of Thames - it started at 17:10 and 5 minutes in the switchover happened and the ad break was LWTs. Either one company fed it down the line to the other or they both had copies, I'm not sure.
As MarkyMark says it continued when Carlton took over, but as it was coming from the same playout facility the only thing that changed at 17:15 was the teletext channel identifier and the ancillary text service
It's a bit different to midnight though to the example given at midnight - the companies wouldn't want to take over at midnight for a short period and then close down again till the morning.
Yes, and remember LWT would go into Monday morning, and once 24 hour running started right up to 6am (of course by then TV-am had the 06:00 to 09:25 slot)
Going back to pre 1968, I wonder if the GPO even had the ability to perform an instant line switch anyway ?
They were unable to perform that in some (all ?) regions outside London even by 1983, as evidenced by the 09:15 to 09:25 buffer zone between TV-am and ITV that existed for a while.
In the Midlands region I think ATV and ABC both played out from a joint facility in Birmingham (Alpha Studios ?) so the same situation as post 93 in London, (so LNN wasn't a new idea !), but in the north Granada Quay St and ABC Didsbury, and in London ATV Fowey St, and Rediffusion Wembley