1-6 months, natural disasters or economic collapse
Depending on the area and time, ancient Egyptians had access to copper, bronze, and even iron tools.I don't know how you even measure a distance of....say 10 yards and be within a millimter of the exact same measurement on both sides... create a perfect 90* wall that is exactly the same measurement across on the floor as it is 8' up in the air....in the dark, with only oil light and a copper tool softer than what you are carving.
But if you say so....lol.
Limestone is considerably softer than granite, so that could be dealt with using just about anything, including tools made from flint.
For granite itself, bronze and iron tools were the likely choice.
Why would you assume they worked in the dark? Most pyramids were open to natural light until they were completed. The various underground chambers had shafts reaching the surface, allowing light in.
Why do we only give them credit for the least effective means, and then use that as evidence of our claims?
Also, why would a "close, but not perfect" measurement lead one to believe that a space-faring race did the work?
Shouldn't their work be accurate to microns, or better?
And why would they choose rock as their medium? Why not pull material from another place on the planet, or introduce steel working, and use that?