In addition to the above, I believe that being able to provide a complete response (in this case, I assume it is a 900-1200 word response) in 40 minutes depends on a couple of factors:
- The number of practice essays that you write.
- The number of times that you have attempted to write an essay under timed conditions.
A general goal that you should probably set is the ability to write approximately 250-300 words in 10 minutes (that is, approximately 25-30 words per minute).
Generally speaking, the higher the number of practice essays that you are writing (which implies attempting different types of Module A essay questions and assuming you are taking these seriously), the more exposure and interaction with not only Module A, but also your prescribed texts that you will gain (in terms of being able to comfortably adapt and use techniques and quotes to answer different essay questions).
From experience, attempting to write your essay under timed conditions is a good way of simulating the pressure imposed by an actual exam setting, allowing you to systematically increase your writing speed as you start to write as fast as possible. This is particularly useful if you are planning to use a pre-planned/pre-written essay, but can also be a good strategy to implement after having attempted multiple practice Module A essay questions.
I hope this helps!