Unless if you finished way ahead of schedule, don`t worry about major revisions like reorganizing the structure of the essay–it`s better to hand in an essay with an imperfect structure than a paper that`s impossible to follow because you had to stop halfway through the revision process.
Although the conclusion paragraph comes at the end of your essay it should not be seen as an afterthought. As the final paragraph is represents your last chance to make your case and, as such, should follow an extremely rigid format.
On the topic of planning, it`s important to sketch out an idea of how long you want to spend on each section of your essay. If you know the number of paragraphs you`ll need to write ahead of time, you can do this before the exam even starts!
If you have enough time left over, read your essay again and make corrections. When you`re working under time pressure, it`s easy to make grammar mistakes or produce hard-to-follow sentences; the final few minutes are your chance to clean up those errors.
Remember the paragraph-based schedule we discussed above? It`ll be useless if you don`t do regular check-ins during the exam. Keep an eye on the clock to ensure you`re always on track.
Some students react to the time pressure of essay exams by scribbling down their introduction as soon as they`ve read the question and figuring out their points as they go. While it might seem counter-intuitive, taking five or ten minutes before you start writing in order to draw up a plan will be an enormous time saver.