Getting,
In primary, we think of registration time as a time when certain (often squeezed) parts of the curriculum can be delivered, as well as when key pastoral issues are dealt with.
So the curriculum for registration time - like, for example, the coverage of assembles - is carefully planned as part of the whole school timetable, both in terms of the whole class and a key time for provision for those with SEN, whether learning or behavioural.
From my observation of DC's secondary, they think about it the same way, and subjects like citizenship, RE, anti-radicalisation agenda, drugs and alcohol education, careers advice, study skills, preparation for work such as CVs and interviews, mental health provision such as knowledge of relaxation techniques, as well as key skills like extended reading, knowledge of key facts, speaking to an audience, and provision for those with SEN, are all carefully planned into the registration time timetable (along with some less structured sessions for purely pastoral work). That then means that nobody assumes such things are 'covered in lessons', and frees up those lessons for subject content and skills.