more on sleep

I'm not sure if this is a sleeping disorder or not but as spring approaches I sleep less. It's the opposite of Seasonal Affective Disorder.  I think it's due to how fast the daytime sun changes this time of year.  The day-length follows a sine curve.  At winter solstice we are at the bottom of the curve (shortest day of the year) and it's relatively flat, so daytime length changes slowly.  Same thing happens at summer solstice when we are at the top of the curve (longest day of the year).  During the equinoxes we are are at the points where the daytime length changes the most every day.  Right now, sunrise is changing by 1-2 minutes per day where I live (Wisconsin).  On March 21 it will change by 2 minutes per day.  Back in December it didn't budge for several days.  I think this change of sunrise is what makes me wake up early, moreso than the actual time itself.  It's just a guess, but all I know is, every spring I get a bit of insomnia.  I still sleep okay but I wake up early and I feel pretty energetic.  I don't seem to mind the lack of sleep.  But I fear it's unhealthy since I'm told I should get 8 hours a night.   I probably sleep closer to 6-7 hours per night.  Sometimes 5 though.  rarely more than 7.