I'll keep this brief for now.
A little bit of oversleeping happened the morning of day 7 (okay, it was 4 hours) but it didn't throw me off.
The night of day 7 (also the start of day 8) I went out to a nightclub. To make this work I napped from 9-9:20 PM as usual, and then again from 2:30-2:45 (the club closed at 2). This stretched the time between two naps to 5.5 hours (beyond the usual 3 hours and 40 minutes), but I was fine. At no point in my dancing did I feel energy-deficient. :)
That second nap came about from walking around the casino and finding a large section that was empty all but for one guy sleeping on a comfy chair. I took the hint and did the same. I definitely didn't fall asleep as I could pay attention to the music playing through the speakers the whole time, though I've found that if one nap in a day is like this the consequences are minimal, if any.
I've generally found it tough to fall asleep in upright chairs. Nevertheless, I'm glad to have found a nice public-sleeping spot-- indoors, nonetheless. When I woke up a woman was sleeping in another chair nearby, and the original guy I saw was still there. Perhaps the polyphasic disease is spreading. :)
I also drove home at 3:30 AM with no problems, though driving for another 10-20 minutes would have been dangerous due to tiredness. Going out certainly made getting through the night much easier than usual. I definitely will spend another night out of the house during this trial.
Later in the morning of day 8, at the 7 AM nap, I accidentally slept until 8. This was the 3rd time I had overslept during this trial. I learned the hard way that, while oversleeping doesn't have to fry my schedule it can fry me. I felt horrible-- a truck might as well have hit me. The bags under my eyes were massive. I managed to distract myself just well enough to reach the 9 AM nap.
Based on this, I've considered that I should seek to recharge or restore myself rather than sleep through these naps. I can't want sleep in the way I've always known it. Sleep is far more practical than it is comforting-- though, when I wake up from a nap I get the sense I've been asleep for at least an hour, so I guess I get the illusion of sleeping at length. Right? ;P
The night of day 8 I took a nap in my car and it was surprisingly restorative: I actually fell asleep. This may be because the driver's seat of my car can be made to lie completely flat, unlike other cars I've tried sleeping in. :)
On day 9 I ran a 5K road race and my finishing time was one of the least impressive I've pulled in the last year, though I also did not train much. I didn't feel, during the race, like my sleep schedule had much to do with my performance-- I certainly wasn't sleepy. Then again, I can't be so sure. :P
Overall, this sleep schedule is steadily becoming less difficult to maintain. Varying the time between naps has become easier. I fall asleep quickly on an increasingly-consistent basis. I still take 8 naps per day and am unsure whether I will drop to 6, but for now I am comfortable with 8.