Is the use of ‘in’ and ‘under’ in the phrase in ‘one’s dizzying journey in under a year’ redundant?

Solution 1:

@Colin describes the grammar of the sentence very well. Additionally, the nuance of "in under a year" as compared with "within a year" is that the former emphasizes that the journey took less time than might be expected.

For instance, if I say that I journeyed from California to Maine within a year, that's not remarkable; it takes four hours by plane or four days by car. That should be easy to accomplish in any given year.

However, if I say that I walked from California to Maine in under a year, that is quite a remarkable thing—it should take much more time than one year to accomplish such a feat, but I had done it much faster.

So the implication in this sentence is not just that the transformation from reformer to consigliere is unexpected, but that such a change occurring in less than a year's time is really remarkable.

(NB: I don't actually know how long it would take to walk across the US, but I imagine it would take a long time.)

Solution 2:

It's not redundant. "In under a year" means "in less than a year", or "during a period less than a year".

"In" introduces the prepositional phrase. "Under" is here not really a preposition, but a quantifier.