Oh come on people, cut them a break, they're Irish. I doubt if they had MLK's whole life crammed down their throats in school like Americans do. They're kind of old anyway. He probably died when they were in their early teens.
When you write a song about an actual event you should get your facts right about the subject. How is "early morning April 4th" any more artistic than "early evening April 4th"?
I'm a U2 fan and I know perfectly that the song "Pride (In the Name of Love)" is from the album "The Unforgettable Fire" and not "The Joshua Tree". It later appeared a live version in "Rattle and Hum" and it was essential in compilation albums like "The Best of U2 1980-1990" and "U218 Singles" but it never appeared in "The Joshua Tree". So, there's a slip-up and not the one you mentioned. "Early morning" sounds much better than "Early evening" or "Late vening" in that situation. And in a song, the things don't have to be the exact way they are.