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Use a planetarium program like Stellarium set for your correct latitude and longitude.
Enable azimth grid and use the ctrl - or ctrl = to cycle the time backwards and forwards. In the winter you will see that the sun is never due east or west. At the equinox the sun will rise and set in the east and west. In the summer the sun will rise and set south of the east and west points so it will cast a shadow east west at some time.
That time can be read directly from the display as the time the sun is on the 90 or 270 grid line. At this time the shadow will be East or west.
Barry
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