We started papers in the summer or just before the summer.
What I found useful when I started was doing the maths paper myself and you'll be amazed at the speed you need to work at to finish in time ( I didnt). Its also helpful for you to do the paper because it gives you an idea of what you need to teach your DC. I only did the NVR and VR after studying the textbooks first.
Papers are mind boggling and you really dont want to do them too early. My daughter was so fed up with them by mid august and only did one set after that. You want them to peak at the right time. We did about two sets in May, that was really to see how much she knew and her weakness areas and also just basic preparation for the mocks she did in June. I dont think we did any more papers until end of July to Mid August.