I haven't heard of their being any benefit to day/night temperature fluctuations. Generally we keep temps at the higher end of fish's comfort zone (summer time levels) to encourage breeding. Certainly a fish can withstand temp fluctuations but I haven't heard anyone claim evidence that doing it nightly is of any benefit.
There seems to be some disagreement on the topic which is why I reached out to hear any actual experience. The primary benefit mentioned in this article is related to immune system health. I'd love to see some actual research on the topic, but have not found any thus far.
I think species of fish is a big consideration here, and South American species from the Amazon are probably not good candidates. Other fish species from regions with bigger temperature fluctuations might be a different story though.