I passed the PMP exam in July 2011 and found the Prepcast tool invaluable in "topping up" my base knowledge, and reinforcing key knowledge areas. My study repertoire included Rita Mulcahy's RMC PMP exam prep system - this was my initial and base building source - and I also added the PM Prepcast toward the middle-back end of my study period, to act as a supplementary resource.
The easily digestable content, structure and learning style suited me and my study plan perfectly, and found I was listening to podcasts on my commute to and from the office on most days. I also used travelling time in the car as a listening period.
I allocated a study block of 7 weeks to preparing for the PMP exam. Wks 1-4 were spent reading & digesting the RMC PMP exam prep system, and I added the PM Prepcast in Wk 5 - which basically gave me 3 clear weeks to focus on this.
To borrow a sporting term, I focussed on the "1 percenters". Even if I only had 10 minutes available, I listened to a portion of a podcast, as I figured this was better than nothing! At the end of the period, the "1 percenters" quickly added up to a significant chunk of quality listening & digesting time.
So my best advice is to capitalise on the available time you have, even if it's just 10 minutes. The PM Prepcast is a perfect solution for these times!