Yeah, the time dilation effect due to shrinkage is no joke in that nano verse arc.
Not sure if even when that Spider-Man arc appeared it was meant to approach THESE levels:
Source: Superman/Batman #58 (and/or 59)
Say what you will about the quality of the final product, but the ideas of the S/B title could be fascinating, even if it were merely that of exploring differing character perspectives:
As for Superman being potentially dangerous even at "Despotellis" scale, though?
No problem. Just be sure to give him shrink treatment on the level of what Spider-Man got; there's a point at which even "indestructible" bullets are so small their flight paths become a thing of no account even when several million of them go through you (Neutrinos work on similar principle, if memory serves).
Either SpiderArc OR SBNanoverse treatment leave Superman a harmless bit of quantum trivia:
