Exactly. I'm in the same boat, but I was prepared for it. I've been guilty of thinking the building of the product was the hard part. Convincing others of using your product is the real work.
An announcement on HN or PH is not going to do it. And it would probably only be a temporary spike if it did illicit interest.
My goal? Hang out where those who may be interested in my product are. Scan and search HN for relevant posts. Find relevant subreddits. Contribute to these communities, and don't only promote your product. At some point, there will be excellent opportunities to bring up how your product is an answer to a particular questions or problem. And it will be appreciated and you will hopefully get feedback and criticism.
There's all kinds of value from this – not just getting users.
Reality is that nobody will visit your site after you launch and you'll have to work really, really hard at getting those first few customers.
I've put my hopes into the 'launch rush' before and was crushed when it didn't happen. (Twice, actually.)
You built the MVP, and that's an awesome milestone, but that doesn't mean the hard work is over -- it's only a start of a different kind of work.
Just pull the trigger and deal with issues as they come in.