The only guideline is what's best for you to get the most out of it in terms of learning experience. What I did was to listen to it once or twice in its entirety. Then I would play each part as many times as I needed to understand what was being said. I would also listen to the solution and make sure my eyes could reconcile what my ears were hearing. Then, in the end, I would listen to the entire text again, with eyes closed. It was amazing how much more I was able to understand once I had completed the exercise. It's always important to end a lesson on a positive note and with a feeling of accomplishment.

Thanks, much appreciated.