After Della gets $20 for her hair, she hurries to shop for Jim's Christmas present right away. The story uses the metaphor of hours flying by to convey Della's eagerness and delight:
Oh, and the next two hours tripped by on rosy wings. Forget the hashed metaphor. She was ransacking the stores for Jim's present.
The verb "tripped" is used here to mean "skipped" or "stepped along lightly and quickly." "Rosy wings" suggests that the hours are flying along as delicately and quickly as a butterfly or bird; that's an awkward fit with the word "tripped," but the metaphor as a whole could perhaps refer to flight—it's not entirely clear.
The next sentence clarifies the purpose of the phrase's awkwardness. The adjective "hashed" means jumbled or messy, so by urging readers to disregard the "hashed metaphor," the story actually draws attention to the fact that the metaphor doesn't work smoothly. This is an unusual move that fits with the story's overall chatty, intimate style and the narrator's playful, self-deprecating tone.
The point, then, is that the metaphor doesn't work very well from a technical point of view, but it does convey Della's mood at this point in the story: she's so excited to buy the perfect gift for Jim that the hours pass quickly and happily, even though she's just gotten her beloved hair chopped off. Even the tragedy of having to sell her hair can't get in the way of Della's excitement to show Jim how much she loves him.