During the Writing paper, you will need to complete two compositions. Both texts are the same amount of words and worth the same amount of points. Therefor, you should try to spend equal amounts of time on both tasks. On the C1 Advanced exam, you should aim to spend around 45 minutes per text. 

Make sure that you give plan to both plan and check your work. Planning will actually help you write faster and will result in better pieces. 

Suggested breakdown per task:

• 1. 1. Planning - 10 minutes

     2. Writing - 30 minutes

     3. Checking - 5 minutes

A lot of people want to skip the planning stage and immediately start writing. However, this often leads to disorganized essays and can lead to frustration. It's actually much wiser to plan your writing.

Having a plan will:

• help your piece be more organized, leading to a higher mark for organization

• help you with idea generation 

• make it easier to double-check that you've done everything required in the task, leading to a higher mark under content

• make the writing process will be much easier and faster

• result in writing which is easier to read, leading to a higher score under communicative achievement.

Planning is actually really easy and not a waste of time at all. In fact, all high-scoring pieces begin with plans.