As a drama, “Good Night, and Good Luck” is decent and earnest, the equivalent of a well-crafted pay-cable docu-movie. But as an alarm, its tone is keening and its timing supernaturally perfect.

Decades before CNN agreed to Saturday’s live telecast of Broadway’s Good Night, and Good Luck, George Clooney had originally envisioned it as a special for CBS, not a movie for theaters and a ...