When ITV opened in 1955, shows were broadcast all day - until the dire financial situation kicked in and the daytime schedule was axed. There were daytime serials, magazine shows etc... The more restricted schedule - that lasted until 1972 when the daytime service launched, must have come later.
I think the misunderstanding of your post is your reference to "all day" because of course Parliament restricted television's hours of transmission and programmes certainly didn't appear "all day", but were spread across the day. Associated-Rediffusion made the most of what they had by running some morning programmes, then half an hour of test card, then more programmes. Then more test card. And after children's TV there was an hour's gap. When Lichfield opened, ATV didn't bother with morning programmes and started at 4pm instead.
The "Schools programmes suspended" caption relates to an ACTT dispute. Any breakdowns in schools programmes in the days when they were shown on the local ITV station would be covered by the announcer, because the union ruled that as long as the station was on the air their had to employ a live announcer. (I was the national union negotiator, so I remember fighting hard for this rule at the time.)
The views expressed on this forum are entirely my own.