The correct answers are It was not until midnight that the thief bypassed the security cameras. and It was from the hidden safe that the diamond was actually stolen.

In an it-cleft sentence emphasizing a prepositional phrase (like from the hidden safe), the relative clause must be introduced by that, not where or when.

Additionally, the distractor "did the thief bypass" incorrectly mixes an it-cleft with negative inversion. You can either use an it-cleft ("It was not until midnight that the thief bypassed...") or negative inversion ("Not until midnight did the thief bypass..."), but never both at the same time!