As far as the two second arming "requirement", it was common for armorers to adjust the arming timing before a low level mission by spinning the fuses in a predetermined number of turns. As far as safety goes, the Eighth Air Force had a couple of bad accidents before D-Day due to dropping fused bombs while loading so it was decided to not install the fuses until the bombs were loaded. They had one explosion the following spring so bombs could still go off without fuses installed.