How do I structure an essay well if there is only a limited amount of time to write it?

It is important to take a little time - around 5-10 minutes depending on the length of the exam - to sketch out your argument, making sure to cover all of the AO's. Remember to include the broader historic context, showing that you are aware that texts do not exist in a vacuum, but are part of an intricate network of influence that shape the text as much as the author. Remember to make sure that you are clearly answering the set question. No matter how good your quotes are, they will only really be useful if you can show how exactly they are relevant to what the examiners are asking.

You do not have to adhere to your initial plan precisely, but it will give you a rough path to follow and prevent you from losing sight of the question or the argument on the way.