How close to the edge can I place a hole?

According to ASTM 1048-04, any hole in the glass must be placed 2 times the thickness of the glass from the edge of the glass to the rim of the hole.

If you are near a corner, the hole must appear a minimum of 6.5 times the thickness of the glass from the corner to the rim of the hole.

So if you were working with 1/4" glass, the hole would need to be a minimum of 1/2" from the edge of the glass, or no less than 1 5/8" from the corners.