Biphasic Sleep Update: Switch to 90+270 Schedule
After some research online, I'm having a hard time believing that three sleep cycles (as in the 90+180 schedule that I have been on) could be enough to live on healthily. I'm going to switch to the 90+270 schedule (four sleep cycles), extending my nighttime nap backward to 12:30am to 5am.
BSper: Actually, what I've read suggests that from the beginning your sleep cycles are around 90 minutes (slightly different for each individual, though), with no need for adaptation or sleep deprivation. The cycles do differ from each other in any given night in terms of the ratio of NREM to REM sleep--more NREM in the first cycles, more REM in the later cycles. That might explain why your source is saying first REM sleep might not occur until 2:10, though I'm not sure. Could you post links to a couple of those sources?
As regards waking up in the middle of the nap, I think that'll go away over time once your body gets used to it. Probably going back to sleep was the right move, since you're telling your body that you want to sleep the whole 90 minutes.