Read this story 20-30 years ago but it was probably old then.
A team of operatives (from the future?) tries to influence the actions of one key man to prevent devastation of earth. In one world this man is a high-handed snob...I remember he’s ordering breakfast and the waiter asks him if he wants fries; our protagonist frowns and says, “It is Wednesday” ... apparently that’s a holy day In this timeline and fries are forbidden then. And he and another man bump into each other accidentally and a duel ensues.
Can’t remember the second timeline, but the fries incident and the duel repeat, I think.
The last is basically 20th century US and our hero is just a regular guy. “Fries?” “No, thanks.” Bumps into the guy, both say “Sorry” and go their way.
Does this ring any bells with anyone?