What is the topic? For my exams, I spent around 8 hours per topic for notes and then more for revising, but I am in Year 11 so really need to cement the knowledge.
Just start in the morning on Sunday and work for a bit until you know it. Then spend an hour on Monday going over it. It's important to realise you can't set a time for studying, as it takes people different times and sometimes you can't work as effectively. If you're good at memory, it will take less time. If it's a short topic, it will also take less time.
Hope this helps.