I spent over an hour trying out all the free "time of sunrise / sunset" apps I could find (there were around 10 of them), and this is the one I think is the best, for the following reasons:
1) It acknowledges and provides useful info, in layman's terms, regarding the fact that it gets bright before sunrise, and stays bright after sunset
2) It allows one to see how sunrise & sunset will vary as the calendar varies (the daytime/nighttime "clock" display changes as you change the date)
3) It automatically determines your location, but, according to the support page, allows for manual setting if, for some reason, the automatic method fails (it didn't fail in my case, so I didn't get to try this out)
4) Except for a brief mention in the help section about an upcoming version with an extra feature or two called "this app Plus", there are no ads.
5) The times are accurate
6) There's an easter egg in it having to do with the moon. Visit the developer's support page for info about that. I think he's cool to have this little feature, but not to boast about it in his iTunes writeup.
The only minus is that the graphics are plain, not fancy - but that is not enough of a negative to cause me to subtract rating points.
Five stars and job well done!