Meaning of a mixed metaphor from "The Gift of The Magi"?

This is from The Gift of The Magi by O Henry (William Sydney Porter).

Oh, and the next two hours tripped by on rosy wings. Forget the hashed metaphor.

(part 4, paragraph 5 in the reference above)

I fail to understand what the hashed Metaphor is, in the context of this story. Apart from this line, the rest of the plot is clear to me (and so is the context). I found a reference according to which the metaphor was actually a mixed metaphor, but I am not well-versed with the types of metaphors and their relative differences (or meanings). I also went through a reference which stated that this metaphor might have stemmed from the fact that this story was written while meeting a strict deadline. I fail to see the connection between the meaning of this metaphor and the haste with which it might have originally been written.

One of the definitions of hashed in your reference is "mangled" (combined in a haphazard way; contorted and damaged thereby).

The metaphor is describing how time passes: it "tripped by" — that is, with dainty dancing steps — on "rosy wings". While time does fly according to one turn of phrase, the juxtaposition of flying and stepping is what causes the mixed metaphor.

With regard to haste in writing, it has nothing to do with the metaphor itself, but with including it at all. Because of time pressure, Porter had less opportunity to self-edit and eliminate the mixed metaphor.

I think the primary intention here is a jocular breach of the fourth wall. Any author capable of spotting mangled metaphors is capable of coming up with less defective ones, unless it's all part of the game.