Using a hammer drill and diamond drill bit - how long does it take to drill through a 12" limestone?
Limestone is usually a soft stone. I'm not sure what you mean by a diamond bit, but my standard hammer drill bits would go through 12" of limestone with a 1" hole in 2 to 4 min. Note that the entry hole will be clean but the exit will crater out. Minimize the crater by setting the stone firmly on damp sand and go easy as the hole nears completion.