I think it's important to point out that 520 is a 38th percentile score. So, when you speak so disparagingly about this score, you potentially alienate a large number of people viewing this post.

Okay, regarding the likelihood of achieving that 700+ score: sure, this is totally possible. Just check out the many success stories in this forum to see what I mean.

As far as when to take the test, I typically suggest that students achieve their target score on at least 2 practices tests before they take the official test. So, you might want to wait a bit before you schedule at test.

Finally, you benefit from signing up for BTG's free 60-Day Study Guide (https://www.beatthegmat.com/mba/gmat-guide). Each day you will receive an email with a series of learning activities that will guide you, step-by-step, from Day 1 to test day (an outline of all 60 emails is here: https://www.beatthegmat.com/mba/gmat-guide-outline).

Cheers,
Brent