Thank you for posting here. It is absolutely possible to jump from one training mode to another as you desire and in fact, we highly recommend doing this as we understand that different people have different preferences when it comes to learning.
So if you are more comfortable answering a few questions first, you can opt to do some tests in the Review Mode as it randomly generates 30 questions from a given set every time you load a particular test in that training mode. You can then move on to Timed Mode if you want to simulate the actual exam environment.
Either way, the goal here is to provide you as much training modes as possible to help you not just pass the exam but also learn a lot and become a competent AWS professional.
Hope this helps and enjoy learning at the Dojo! 🙂