@bellinisurge,
But what do you want to know FOR? It does not seem to be idle curiosity.
There are so many different models of schools with so many different priorities. The current trend is actually for fewer GCSEs and more ‘enrichment’.
But, you can fit in more GCSEs with fewer (or no) study periods, which just means a long evening of homework. In addition, you can have longer or shorter days and longer and shorter lunches.
Ultimately, though, a gcse requires a certain amount of hours spent to do well in it but this does also vary by child, especially in subjects like maths, which can take minimal work for some (who just ‘get it’) and hours of painstaking toil for others, who attempt to ‘learn’ it like a humanities subject.
It is such a complex and multilayered question.
And, as for ‘challenging it’, it will be a total non starter. Virtually all state schools cover the natural curriculum. Over and above that, they are free to teach (within reasonable bounds) what they see fit. On what grounds could it be ‘challenged’?