GMAC official practice tests do not show you the timing you took per question on the results and this is a huge issue. To solve this, use any screen capture software to record your practice test while you take it. This will allow you to see where you spent the most time etc. which is key to understanding how to improve. Moreover, your essay will be also lost after you take the practice test and you can't go back to read it. If you have been recording, you will also be able to save that.
Hope it helps.
Ps. Some of you know that I've been live streaming my study at twitch.tv/gmat800 for the past 1.5 months! I'm currently on the 760 range on my official GMAC practice tests, trying to keep polishing to be ready to kill this next Tuesday. Thanks all of you who have been supporting. You can also ask questions in our discord community:
https://discord.gg/2DQRpkv