When I studied for university exams, I used two-phase sleep cycle. I studied from 10 AM to about 3 PM, then I had a 3-hour nap to about 6 PM, and then I continued to study from about 7 PM to 11 PM.
I can wholeheartedly recommend it; it's quite efficient and you can easily adapt to it from your normal single-phase cycle.
I'm sorry but you didn't provide enough data on your sleep. Basically you're telling us you took a long nap in the afternoon. How much sleep did you get at night?
Well, this was like a decade and half back, so I don't have "enough data". :-) You're right, that's what I am saying. I think I just got the amount of sleep I needed at night (which means I woke up at around 7). This is not a technique to reduce sleep, but to learn better.
I can wholeheartedly recommend it; it's quite efficient and you can easily adapt to it from your normal single-phase cycle.