I would say you would need the same amount of time to prepare as you would doing the written test in person at the DMV. One thing that can help you check if you are ready is do to an online practice test. There are different ones available online, such as: www.tn.gov/practice/ or even better, the DMV has its own practice test you can do located at: www.dmv.org/practice-permit-test.php. You could even try both, and if you do well on them, you can be confident you will do well on the real thing.