Question: Since when do they execute people so quickly on death row once the corrupt cop is exposed for being the real killer?
Answer: Time passes quickly. It doesn't show every minute of every day. When he was executed, several months, maybe a couple of years, had gone by. They wanted to show him finally deducing that Clark Kent was Superman.
Deliberate mistake: Season 2, episode 6 "Identity Crisis": When Bizarro starts decaying into the parody form of Superman, his costume goes with it; the blue fades, and even the 'S' insignia changes. Strange that superhero garments change right alongside their wearers when they suffer from an unstable genetic effect. Were the clothes cloned right onto his body, instead of sewn?
Mxyzptlk: Your three months are up! And this time you're not gonna cheat me of my fun.
Superman: Oh, it's you again, Mr. Kltpzyxm.
Mxyzptlk: NOT Kltpzyxm! Mxyzptlk! Now,  the first thing I'm gonna do - ah, nuts! [Disappears.].
Trivia: When Kyle is knocked into the airfield by Siniestro, he crashes into a Sabre jet. As he recovers, we read the pilot's name as Col. Hal Jordan. This is the name of the second, Silver Age Green Lantern.
Answer: To add to the other answers, in the U.S. the average time on death row before execution is close to 20 years due to lengthy appeals, legal challenges, evolving state policies, and complex judicial processes. In modern times, it never happens as it does in movies and TV.
raywest ★