Nothing special,

At noon (local time) the sun is due south er sorry north for you <img src="images/graemlins/blush.gif" alt="" />. It moves 15 degrees per hour. So if the sun is at 345 it's 13:00, 330 it's 14:00, etc. Accuracy is as good as you can measure the angle. Quarter hour should be entirely doable (i.e. 3.25 degrees). A bit more difficult at night of course....

That's how sundials work, they are just fixed compass cards aimed due south (or north). (although on good ones the pointers are also set for a certain latitude as well to get optimum shadows).