I believe it is two years since the launch of the title.
EDIT: Sorry, I misread the post, thought you were talking about the coin rewards with games.
EDIT3: I believe this guy got a similar answer
Lmao , love how you posted my thread on ERA for the same question.
Thanks! Yeah it doesnt show any expiration - I just wanna finish my run of Super Mario Odyssey before I redeem the code so I can take advantage of the NSO NES and SNES games.