If you are willing to do a bit of compiling (no dependencies, no nothing), you can download the source code for such a program from NIST: ftp://time.nist.gov/pub/daytime/
You may want to read a bit about the time standards at http://www.boulder.nist.gov/timefreq/service/its.htm
README file it's said that you should use two files (except for the Makefile) to compile the program. However, they can be copy/pasted so you end up with only one file to compile (and you eliminate the need of the Makefile).
Once you have the executable, you can start it automatically with an init script or run it on a regular basis via cron.