Yes - when you click on the link you can view the introductory videos, get set up and take a practice question as many times as you like. You can leave the process and return at any point during this part of the video assessment.
Once you proceed past the practice question, you should not leave the video assessment process. In some circumstances, seeing a question and leaving the process will mean that you can no longer answer that question. We'd strongly recommend that you proceed to the real questions when you are ready, and answer them all in one sitting.