[Keith]

How many rehearsals do experienced presenters need? Can’t imagine more than about 15-20 hours.

I imagine that the rehearsals aren't just for the presenters benefit.

They'll presumably want to test out the new proposed schedule to see if it works, particularly around UK/global opt-outs and advert breaks. Rehearsals can confirm whether what should work on paper works in practice and in the event of problems how big or small the issue and solution may be. The solution might be a simple as needing to practice it a few times or as extreme as completely re-writing parts of the proposed schedule.

Far better for everyone that issues are identified and resolved off air in rehearsals, than having them occur on air.