I seem to remember the lemmings move a little bit faster on NES compared to traditional versions like Amiga and DOS, although it's maybe also possible the in-game timer also moves correspondingly faster as well, I don't remember about that part. Either way, I hope the NES recreations, if keeping time limits, take into consideration that aspect and have actually tested the levels accordingly, so that generous time limits remain generous and tight ones still achievable, on the recreations in NeoLemmix.