> And to act like they are not worthwhile life pursuits because they aren't pushing humanity forward is a nihilistic viewpoint because it's focused on spending my life so that after-my-life benefits as if that makes it more morally correct.

What's so special of minds that exist at a later time? Note that under special relativity, spatial separation and temporal separation are relative to frame velocity. In effect, they're basically the same -- other minds, at other places in spacetime. If you accept that minds other than yours are important (as important as yours -- otherwise, what makes you so special to be the only consciousness that matters?), then you should help whether they are now or at some point in the future (of course, there's the question of reliability of impacting the future, but those are more practical questions).

As others mentioned, I don't see how this ethics identifies with nihilism and even less Nietzche's nihilism.

Your view seems more like akin to solipsism: the denial that other minds exist/have value as well. There are strong arguments against solipsism from computational theory of mind (which I may have discovered, I need to publish those).

If you're interested in this kind of stuff, I'm working on a formalization of ethics that aims to answer this sort of question more helpfully and precisely than we've been historically (for now all I have to refer is a subreddit...).