In the context that practice responses are like past paper questions and preparation, and not simply revision questions.
I believe that practice questions should be done after you have mostly mastered the content or around 3 weeks before an assessment.
In the contexts of prelim and hsc, I am not sure however I think it is likely just that resources for prelim aren’t as extensive as for HSC as practice responses and past papers tend to vary across schools for Prelim, resulting in less practice responses available and thus needed to be done.
However keep in mind, this is just a personal opinion. Try different techniques to see what works with you as after all everyone’s different.