Take it when you are comfortable. Try to avoid early mornings if you're not accustomed to them.

i ma also planning in mid of august. why not in morning hours. i found that my speed of problem soving or verbal is better than in evening hours. i find sleepy mood after lunch. i think better to start at 9 and finish it by 1 pm then enjoy yr lunch

Choose the time when you do your best work. Try taking practice tests at the different times and see whether one works better for you. For many people, it doesn't make a difference.

Whatever you do, be sure to get your body on an appropriate schedule. If you plan to take a morning test, get up at the time you need to get up for the test for several days ahead of your test date. Don't sleep 'til noon all week and then expect to do your best on test day when you have to get up at 7:00.