In the poem "People on the Bridge" written by Wislawa Szymborksa (Translated by Joanna Trzceiak) the phrase "Time stumbled and fell" is used. Is this an example of a juxtaposition used by the poet?
Chambers online defines juxtaposition as
placing or being placed together.
Lexico goes a bit further and provides the definition
The fact of two things being seen or placed close together with contrasting effect.
I don't see any of that in the sentence you give us. Perhaps you are searching for the word metaphor which is probably a fair description of the idea of time stumbling as if it were a legged animal rather than, well, something rather more abstract.