Probably subconscious. I tend to use "instant" when trying to sound more technical/physics-y and "moment" when being more conversational. If time is emergent, both words are describing the same phenomenon.
It's like the difference between saying "temporal coordinate" versus "when", one sounds more scientific but they're pointing at the same thing.
This might be a really dumb question, but how do you use "temporal coordinate" in a sentence where you would use "when"? For example: "When I walked my dog ..."? :D