I have a copy of Major Arthur Hogben's book, `Designed to kill'. Page 99 gives diagrams of a fuze, similar to your photos. They are titled `Italian bomb 4AR (Thermos)'. `4AR' stood for `4 kg Armamento Retardato', delayed arming bomb.
Before the bomb was dropped the safety pin was withdrawn, allowing the vanes to rotate as the bomb fell. The vanes were part of a cap and once unscrewed, the cap fell away from the bomb. Air caught the projections that stick out from near the top of the bomb and pulled off the cup from the bomb, releasing the primary safety devices from the fuze. The bomb fuze, still falling, now looks like the fuze in the second photo. On initial impact with the ground the secondary safety devices were released and after a few more seconds the bomb was fully armed. The bomb could then detonate when jerked or jolted. An alternative fuze version incorporated a timer (type not stated, but presumably clockwork) that could be pre-set to detonate up to 80 hours after impact, even when left undisturbed. An area denial weapon, then.