I can't remember where I read this prose story, but in it there are super heroes. One of the super heroes can travel backward in time, but experiences all of the time that they travel through (so traveling 1 day back would cause him to experience 1 day of time in limbo.)
The hero ages faster because of all this time spent in limbo, but he also gets bored, and tells jokes to himself to pass the time.
He wasn't the main character in the story, but was a viewpoint character at times. I think I read this online.
Edit: I recall the main character was a different super hero who did not dress in a costume (and did not have a secret identity). He has a normal name (like Bob or Joe), and his super hero name was something like "Amazing Bob" or something like that. I believe he was considered powerful in the story world, and I recall a portion of the story where someone clones him a lot (4 times?) and makes the clones try to kill him. The story was named after the main character, and his super powers were pretty much similar to Super Man's powers (flight, speed, strength, laser vision, etc). Additionally, the story was named after the main character, and the main character had money problems and had to keep a day job because people never paid him for his super hero work.
The main character was just way less exciting than the time traveling masked hero who told jokes. I just also remembered that the time traveler also went back to visit himself at one time in the story and the version of him that had traveled back to see himself was nearly dead, and he had to figure out how to prevent himself from getting killed.
What story is it, and where can I find it again?