Oh I wish I had more time too! For you and other good authors here. You're one of a group I picked to read consistently that's true. Other examples are mountainwashere and effofex. It saddens me that I can't read everything! But then again I haven't even read every work by Shakespeare so...!
The story is good but there's just something about the ending that needs improving or reworking but I can't put my finger on it. The store's security taking him in for questioning almost sounds too realistic, so it's like it doesn't positively incline the story toward the supernatural. It needs a more absurd ending, like having him thrown in a dungeon, something quite unfitting and not rationally justifiable. Something relating to the old man/version would also be appropriate.
Just a few hours ago I finally watched the movie Get Out by Jordan Peele, had it on my watchlist for some time. I feel your story is trying to portray a feeling similar to the one it elicits. And it's interesting that the feeling is maintained even though everything that happens is explained by the end. Leaving it inexplicable is very okay too, obviously, but for example I think I would prefer for Craig to notice that for some strange reason he's starting to age fast, and as he tries to leave the store he finds that for some strange reason he keeps ending up back inside, and the only way to stall his aging is to work behind the counter...something strange like that. So perhaps introducing the evil power as a visible entity in the form of the security guards and store owners made it too tangible and rational for me.
Anyway just brainstorming at 3 in the morning :D
Ohhh I like that too - perhaps it worth a revisiting in the future - that's the thing with writing these for writingprompts initially is that they don't usually have much of a life outside the initial post, and you're absolutrly right that they are often very imperfect, even in the context of simple flash fiction. Sometimes I go back and rework things - this was turned into a first person, creepypasta type thing for r/nosleep for instance, but other times, most times, they just linger in their particular state of imperfect unfinishedness.