Yes, absolutely. This is a diagnostic test reflective of the real test, so you get an accurate prediction of where you are. Get the GMAT Timer
in the downloads section and make it a habit to spend less than 2 minutes per question. This goes for EVERYTHING, when you are doing the OG 12
or any other questions on this forum or in books. It is a good habit to have. If you can't work it out within 2 minutes, then obviously stop the clock and try to work it out as much as you can. Don't give in to looking at answers too early.
tl;dr: Yes, time yourself in all the tests and practice questions you do.
Aim for the sky! (800 in this case)
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