There was an exception to the rule though - Schools programmes were routed through ATV/Central. So YTV would feed Scientific Eye to CEN, and CEN would feed it out to the network. This had the advantages that the other regions could cut up CEN and put their feet up for the morning.
Which would have sounded better if the Regions didn't have to come in do the start-up at 9.25am and then sit around doing nothing until 12.00pm, hoping for a breakdown from ATV/Central.
I also believe that ITV's morning schedule that replaced schools programmes was for a while transmitted via Granada to all stations, starting with The Time The Place promo at 09:25:15 until the end of This Morning, eg. Crosswits from TTT or Lucky Ladders from ANG would be fed to Granada from the originating station, also TTTP itself from wherever it may have been coming from, and the various ITN News bulletins. I remember Granada opting out of This Morning to show regional news updates during the 1993 Manchester bombings, whilst still feeding This Morning to network.
And - in earlier days - the 12:00-12:30 childrens programmes were normally transmitted via one station (eg THS, GRA, YTV) regardless of the originating companies - I assume the short 10 second gap between them didn't make switching easy.
Interestingly, even in the mid 90s afternoon programmes like Home and Away, the Emmerdale/Corrie repeats and quiz shows tended to get scheduled at different times in different regions, even though most/all were showing the same episode. I also noticed that just because say Granada, HTV and YTV were showing H&A at 17:10, they weren't using the same feed - one region could be as much as two minutes ahead of another. I'm not sure if these shows would be played out from various 'hub stations' or not. I assume a region wanting to show H&A at 14:30 would tape it from a station who played it out at 12:55, so would already have a copy to play back at 17:10.
It's also interesting - and puzzling - how one station could 'purchase' an overseas programme (think Falcon Crest or Shortland Street, for example) and either 'network it' or 'sell it on'. When Central bought Shortland Street, for example, did the other regions then pay Central for it when they started showing it? Or would this be a separate transaction with the distributors/producers? When Thames showed Sons and Daughters, and Tyne Tees and Anglia latched onto their feed, how did they 'chip in'? The legalities sound complicated - but perhaps they're perfectly simple?