It's not good writing. There is no authority on language, so "permissible" has nothing to do with it. Writing guidelines are drawn from what makes the communication effective and pleasing to the reader; often this amounts to "everyone else does it this way," which is where the "rules" you learn in elementary school come from. That said, misuse of commas can be very distracting as they can convey a variety of syntactical operations which readers must parse. They are the most distracting punctuation when used in an unexpected manner. In this case the author would do better to use "Every. Single. Day."
/pedantry (few threads seem more appropriate for it)
Typically not for emphasis pauses, though, just for clause or item separation pauses. I find it disruptive to visual parsing when they're used this way because I don't expect it. It's becoming common to use sentence breaks ("Every. Single. Day.") to express things like that, but that bugs me since it implies a falling tone on each word. Personally I'd prefer ellipses ("every...single...day."), but that's not perfect either. Writing is always an approximation of speech.
Comments
It is permissible to use commas to indicate a verbal pause.
It's not good writing. There is no authority on language, so "permissible" has nothing to do with it. Writing guidelines are drawn from what makes the communication effective and pleasing to the reader; often this amounts to "everyone else does it this way," which is where the "rules" you learn in elementary school come from. That said, misuse of commas can be very distracting as they can convey a variety of syntactical operations which readers must parse. They are the most distracting punctuation when used in an unexpected manner. In this case the author would do better to use "Every. Single. Day."
/pedantry (few threads seem more appropriate for it)
Typically not for emphasis pauses, though, just for clause or item separation pauses. I find it disruptive to visual parsing when they're used this way because I don't expect it. It's becoming common to use sentence breaks ("Every. Single. Day.") to express things like that, but that bugs me since it implies a falling tone on each word. Personally I'd prefer ellipses ("every...single...day."), but that's not perfect either. Writing is always an approximation of speech.