I voted March, but that assumes that you know you have a good console on their hands. The Switch launched with Breath of the Wild, and it seemed like Nintendo knew they had a strong game on their hands. (It was essentially the only game featured at E3 2016.) In this situation you get a strong launch month, and then you get a strong holiday season, so you maximize sales that way. This is also a risky month, because, if your console has a disappointing launch then it will be really obvious (like 3DS).
So the safe month would be November or maybe October. All of the console's hardcore fans and going to buy it regardless, so launching near the holidays makes it look like its a hot item, and the press can say the console is in short supply and so forth. But really this is a conservative move. It shows that you don't have the confidence to release outside of the holiday season. I suppose it is better to be safe than sorry though.
curl-6 bet me that PS5 + X|S sales would reach 56m before year end 2023 and he was right.
My Bet With curl-6
My Threads:
Master Thread, Game of the Year/Decade
Switch Will Be #1 All Time
Zelda Will Outsell Mario (Achieved)
How Much Will MH Rise sell?
My Bet With Metallox