Time to Build the Pyramid?
Another pyramid at Dashur actually has a date on the north-eastern corner stone it was laid in the 21st year of the Pharaoh Senefru.  About halfway up there is another date, this time dating to the same PharaohŐs 22nd year.  If the dating is accurate, the maximum between the two would be under two years.  This pyramid is about two-thirds the volume of the Great Pyramid. (Wilson, Crash Go the Chariots, 29)