O. Henry primarily uses the phrase "tripped on by rosy wings" to describe the swift way in which the next two hours pass once Della is able to get the money that she needs to get a Christmas gift for her husband, Jim.
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 metaphor, when read within context, would mean that the next two hours in Della's life were pleasant, went by quickly as it always happens when one is having fun, and gave her satisfaction.
William Sidney Porter was a master of language who loved crafting expressions. Porter breaches the fourth wall and tells the reader to "forget the hashed metaphor" previously explained. He basically asks us to dismiss that metaphor because it would not describe Della's actions quite properly.
Della, rather than fluttering around like the quintessential Victorian wife-angel who would be "tripping on rosy wings," was quite hyperactive and involved in the search for a present for Jim. This is evident when he notes that she was actually "ransacking the stores." For Porter to illustrate Della's actions as "ransacking" means that she was far from mellow and content. The actual definition of ransacking is
to search through (a place or receptacle) to find something, especially in such a way as to cause disorder and damage.
Surely, Della caused neither disorder nor damage. It is also obvious that the selection of this verb may have been a bit over the top just to express how involved Della was in her shopping. Yet, this is O. Henry at his best using language in creative ways and always causing big reactions among the readers that have loved him for generations.
This is a good question. We come to these words when Della sold her hair and went shopping. Here is the context:
"Twenty dollars," said Madame, lifting the mass with a practised hand. "Give it to me quick," said Della. Oh, and the next two hours tripped by on rosy wings. Forget the hashed metaphor. She was ransacking the stores for Jim's present.
Based on this context, it is very clear that "tripped by on rosy wings" means she was happy and excited. She got the money, that is, what she wanted from the beginning of the story, and so she rushed to get a present for Jim.
What makes these words interesting is that it is a mixed metaphor. If she is "tripping," because she is rushing out to get a present, then the idea of the "rosy wings," which speaks of flying, is odd. This juxtaposition gives the impression that Della is very excited and eager, which fits the context well. Finally, all of this shows that Della did not regret her decision to cut her hair. She is really selfless. The story is great, because both Jim and Della outdo one another in love.