Not sure which assessment you are talking about but I will give you a short answer for both types of assessments I have in mind.

First, if you are asking about the "comprehension check", it is a pretty simple task. The aim of this phase is for you to prove that you have a basic understanding of the markets, and how they work, and have knowledge about some of the most common trading strategies and analyses. And more or less that's it. The result should come in a day or two. Pretty quick.

Second, If you are asking about the assessment account to pass the challenge to get a funded account, well that's a different story. Is it hard? Generally speaking, it is not. At least for me. And it should be for you as well if your intention is to make profits with SabioTrade following their trading rules. If it is getting hard for you to pass the challenge, then maybe you should consider spending more time on educating yourself in risk management and other trading-related matters.
About the time, you should not care about that, since everyone has a different trading style. But I would say it's quite possible to pass the challenge in less than a month.