Watched a documentary recently, experimenting with 3hours/day. It was cancelled after a week because the "victim" was showing dangerous side-effects and beginning to show major-organ dysfunction, apparently from the stress caused by lack of sleep.
One cycle of three hours hardly encourages the body to enter REM. That person might've only gotten one 30 min sessions in that 3 hour cycle. Once we have transitioned, our body will be getting four 30 minute sessions of REM.
Again, I want to emphasize that I'm not an expert on this, I've just read a lot. I think my thoughts would align with other polyphasers, though.