It doesn't work at 6:00 unless you know which way to face. At 11am you should have a small wedge, and your left arm should be in the shadow, in order to not point both arms straight behind you. At 1pm your right arm will be in the shadow for the same reason, so you're still facing north.
At sunrise or sunset, it's pretty obvious which way east or west is. At least to a first approximation.
For a second approximation you'll want to interpolate between the equinox and solstice and use that to approximate an allowance for the ~24 degree tilt of earths rotation axis.
That second approximation error is there for all times that are not midday, but reduce to zero as you approach midday.
A third approximation might be to allow to the offset between your local timezone and solar midday. Where I am (Sydney) we are fairly close to the middle of the +10 and +11 timezone boundaries, so solar noon is within a few minutes of timezones noon. Perth on the other hand is way out to the west of it's timezone, so solar noon there is almost 25 minutes off from timezone noon. So "watch north" in Perth will be about 7.5 degrees off "true north".
