In that instant vs At that instant

Question

In that instant, xxx

or

At that instant, xxx

I know that "at that instant" is the more correct way of saying it, but can "in that instant" work as well?

At the instant that he jumped...

vs

In the instant that he jumped...

Would both be correct in that case, if "that" and "the" were switched?

Answer 1

The difference is not spacious, but I think one could draw some useful distinctions.

I would use at when I wanted to denote a point in time at which something happened,

At that instant I fumbled my phone into the pond.

and in to denote a very small space of time during which something happened:

In that instant I saw my phone falling from my fingers and cartwheeling into the pond.

Again, it's a slight difference, and you could use either preposition in either sentence, but as a writer looking to wring the most meaning out of words, I would recommend the above.