Nel's statement is consistent narratively, while this calc is not.
- Nel is literally the guide in Hueco Mundo for both the characters and the readers. Every single thing she says is correct, no reason to believe she's wrong.
- It was stated in the Databook 3 that the mission to rescue Orihime took multiple days.
- Both the characters and the databooks talk about how massive Las Noches was. (Going by the logic used in this thread, it's less than half the size of the small town he lives in)
If we go by the actual interior (which is where we spend the majority of the arc) it shown multiple times that the desert is so big that different buildings can be too far away to see. Which doesn't make any sense if you're going to say all these
unnaturally large buildings and structures are contained within a 3-mile diameter. Every Espada has their own castle in Las Noches, and
they're huge even by Las Noches standards, yet we see that they're all spread apart by so much desert that they're not even visible to each other.
The only thing that backs the calc is pixel scaling panels of Las Noches exterior, when we've already accepted for
Bleach multiple times that
Kubo doesn't draw things to scale consistently, and that it's more accurate to use statements.