It won't work in secondary, with 3 separate and random hours of non contact throughout the working week. If I'm free at half 11, but teaching at half 12, I'm not going anywhere. There's tutor group at the start of the day, a duty at the end to stop arriving later on site or leaving earlier.
I get it shouldn't impact pupils' lessons, and Bridget Phillipson has said it's not about cutting contact time. But it should be, by having more staff. That is more flexible and workload reducing.
I teach a core subject, with a TLR, and still have 5 different classes I'm responsible for. That's 150 kids' work to mark, five parents evenings, five X data drops and forecasts each half term, 150 reports, 5 units to plan for at a time, and the associated numbers of additional needs to cater to, liaise with SENCo about, contact parents for.....
90% teaching with 10% given over to planning those lessons well, preparing resources, assessing work and giving feedback and everything else that comes with the job is ridiculous.