The method depends on whether you want your conditions to be constant throughout the year or to vary according to the time of year.

If the former, then do as BluPhenix says.

If the latter, find a site which gives today's sunset and sunrise times, write a script to access this site and download these times into global variables, set this script up to run in the middle of the night, and then use the global variables to control the conditional jumps. This is what I do for my electronically-controlled curtains and it works flawlessly.