Both my sons did 4 A levels with FM. Ds1 had 5 hours for each subject and Ds2 had 4 1/2 hours.
If they took FM then the children were in a different stream to the normal A level maths group. The grade required was a 7 but both of mine got mid grade 9s. They spent year 12 studying the entire 2 years of A level maths as they had a timetabled slot for "maths" and one labelled "further maths" to show the different teachers. They sat AS maths paper before Christmas as they had finished that content. They started FM in year 12 as the cohort was able to.
If they struggled with maths in year 12 they could move over to the normal slower paced A level maths stream. About half did.
Ds's day started at 8.30 and he had a 2 hour slot for the first subject, then hourly slots and finished at 3.20. His timetable also included 5 hours for free periods, a 1 hour assembly, a 1 hour tutorial (like form time sort of) also 2 hours "enrichment" on a Wednesday afternoon. Each subject had 5 hours of contact time (teaching) per week and Ds finished a lot of his work in class or in his frees. He hardly ever needed to do work at home.
He used his free periods to work on homework and they had a little study group because they all wanted high grades.
No doubt @noblegiraffe who teaches maths and further maths will agree, if your child is used to acing maths easily for GCSE and they struggle at A level they need to recognise when they need to ask for help or do extra work to help them understand what they are doing. Lots were unused to asking and then it starts to slide. So instead of just accepting you got a C grade on the end of topic test, you acknowledge where you went wrong and you circle back to it later to make sure the concept is now cemented in your head. You retest yourself. At DC's sixth form teachers were available every day for 30 minutes at the end of the day for guidance. However, some students will just go home or leave the site in their frees, or piss around on their phones rather than using their time productively.