x-post
I'm totally shocked: if I go to bed earlier then my sleep time is shorter longer.
Data for last half-year, 1 pixel represents 1 minute.
from my G+
Another, less shocking graph says that later I wake up - longer is my sleep time:
Final graph:
It seems that the alarm actually makes me sleep longer (the area to the left of my 'alarm time' is suspiciously empty).