Thanks for your message. The time required for preparation really depends on your interest. As I am into teaching psychology myself at university level, the key problem students encounter in this case is that they understand everything when they give the text book a read, however when you try to recall it later, one finds that you are not able to phrase your answer as powerfully as required. For the purpose undertake the following steps:
1. In your first attempt high light the relevant material that you will learn by heart, including examples and researches(for examples and researches you can use your own words)
2. Learn definitons by heart, number the points in every topic, you should know the relevant KEY WORDS. It is the use of these key words that makes your answer powerful and concise
3.If you are really into it than psychology should take a week/ten days to prepare
4. When you'll follow this method you will find that you are able to recall a greater percentage on your first revision and it gets better everytime
5. The material that you highlight to remember really matters, if you give all the points even a 4-5 page answer is enough