I did a search on this, couldn’t find anything but I am sure there’s no real concrete answer. It seems generally agreed upon the NES launched in NYC Oct 18th, 1985.

From a Wired article: In early 1986, Nintendo expanded into Los Angeles, then Chicago, then San Francisco.

I’ve found “February” for Los Angeles. Does anyone have any confirmed days? How about Chicago? I’m also curious about Canada. I think I found two conflicting dates for Canada, that were off by a lot. Australia and UK would be interesting too.