Planning should take about 5 minutes. At the end, check that you have answered the question.
Your plan should be written in your answer book and then crossed through with a single line. The examiner should see you have planned your answer! It does not matter if it is not neat, although your final answer should be as neat as possible. If you are allowed to type your answer, you should still include a typed plan or a handwritten one with your typed answers.
Examiners like to see that you have thought about the structure and content of your answer before you started writing.