... year's(or 10 years) worth of sunrise sundown times ...

The Earth's rotation is slowly slowing and days are getting longer, but the year-to-year change over ten or twenty years is small. If one were only concerned with 1-2 minute resolution, one could store, say, 62 or 183 sunup/sundown pairs (the day-to-day variation is also small). Since sunup and sundown only happen during certain periods of the day, these times might be stored as one byte each. This is a very small table.

Be that as it may, I'm not convinced one should be concerned with time as much as with light. What does it matter if, in midwinter, the curtains open at "sunup" when the sky is so overcast that it's like the middle of the night? A photocell/light level interface seems more important.

I agree with stevieb: These considerations and others suggest a microcontroller solution. A system running Linux seems like overkill indeed.