I think they can do a solid three-to-four month marketing cycle if they do a H1 release. It's essentially what the Switch got, with wider audiences only being aware of it for less than five months prior to release, if that. The Switch's reveal trailer was October 2016, sure, but I'd argue that the marketing blitz (TV commercials, subway ads, public demos, etc.) didn't start until January 2017.
So if they tie the reveal in with a launch lineup blowout and hit the ground running from there, they'll be fine. The only question I'd have is what a May launch lineup would look like. H1 is already crowded with Mario, so releasing a new 3D Mario game then would feel a little weird, seems more like a October/November release. And it also feels a bit too soon after the Booster Course Pass ended for a new Mario Kart as well; feel like you'd want at least a year between them. So I'm not sure what series gets the honor of having the system's first big exclusive game in that scenario.