Both of my children sleep thru the entire night.
I started working swing shift in October. I'll work 7 nights of 11-7, 6 or 7 (my choice) evenings of 3-11, and then seven days of 7-3, which ends on friday afternoon, and I start a 4day break. Following my 4day, I start back on 11-7 wednesday night.
What does this have to do with how much sleep one "needs"?
I have found that I can sleep pretty much when and where I want. If I have a slow night at work (I'm maintenance, not production- if it aint broke, it dont get fixed), I can catch a few winks, and be good to go all day, perhaps with a short nap in the afternoon. I've found I can coherently function on two hours of sleep for every 12 waking hours.
This isnt long-term by any means- sometimes I just need to crash out and I can sleep for 8 or 9 hours straight. But, for short times, I find I dont really need that much sleep to be functional.
It seems like I do my best on either a long sleep, or short naps. The middle ground gives me trouble waking and functioning. I dont understand how I can sleep 2 hours and feel refreshed, and sleep 4 or 5 and be miserable, like I didnt sleep at all. Maybe its a transitionary period between light sleep and sound sleep.