Depends: are you the kind of person who considers it a good idea to be aware of uncertainty? You'll be perfectly happy with "I'm on the northern hemisphere, it's afternoon, so south must be somewhere left of the sun".

But if you are the kind of person who like to lose themselves in point-something percentage point deltas in small (or unknown) sample size market research, go on, pat yourself on the shoulder for building that makeshift shadow observatory, it will make you happy even if you don't really know where exactly you are relative to the center and natural bounds of you time zone.

only because you'd need to know what time it is to know where south is relative to the sun.