Unless you heavily promote a website, hardly anyone and quite probably no-one will visit it when you launch it. One reason is that without promotion, such as on social media, no-one will know your website exists. It therefore does not matter when your website goes live because no-one will visit it and see it. You can therefore quietly build content, try different themes, add plugins and so on, and get it looking great while it is live.
The question should be, when should I promote my site, in other words, tell the word it exists and get some visitors? It is best to wait until you have a reasonable amount of content before you start seriously promoting it. Around 10 posts perhaps. Then visitors can browse around and maybe find articles they like.