Don't sweat it if you consider yourself to be of less than stunning academic ability.
My course of 15 had a real mixed bag of abilities and backgrounds, but only 4 of them had to resit anything and that was only 6 exams. Not bad out of 210 papers. They all passed the resits at the first attempt too.
Total time in groundschool was 26 weeks including a couple of weeks of solid revision with the instructors.
Your biggest advantage is if you find any of it remotely interesting as this will help you to make the time to study outside of the classroom. Most of it is a memory test rather than a test of knowledge, but there are a few tricky papers where a good understanding of the subject is needed to figure out the answer.