How do you know that you are ready to take the test?

Everyone comes across something new from time to time. And that's true even for the experts you refer to in your post. Keep learning, and take the test when it makes sense for you (keeping in mind the other, bigger, goals you have).

By the way, 680 after just 2 weeks is excellent, and I wish you all the best!

thank you all for your responses.

my plan of actions is to now do tests regularly and track my progress

You're ready for the test when you are (at a minimum) - able to reach your target score on a practice test comfortably.

Do NOT walk into the test room if have not been able to score your target in practice. You can't expect miracles to suddenly happen on test day.

But more important than the score itself --is when you feel confident that you are answering every question within your ability correctly. That sounds easy but in reality - a lot of people incorrectly answer questions that they SHOULD be getting correct.

All those easy and medium questions - those should be 100% gimmies for you. If they are not, then you have room for improvement in terms of not messing up questions that you really should be getting correct.

Next, if you are able to correctly answer some reach questions and feel you are reaching a peak - then you may be ready for the test.