I wanted to post a couple times but as I am still fixing and improving things and never thought that I am ready to post it yet.
There will always be more work you can do. You need to just draw a line in the sand and everything else can be done later.
If you are not embarrassed by the first version of your product, you’ve launched too late. - Reid Hoffman
There is no perfect formula for posting. Some say you should post on Wednesday, 5pm PST etc., but it doesn't mean you will sky-rocket with up votes.
Personally I avoid weekends, but HN is hard anyway (At least I had no luck.).
Any time will do. Someone analyzed best times and posted an article here a while ago, but I've seen show hn's posted on Sunday afternoons stay on the front page till Monday. Just ship it.
Projects are never done. You'll always be improving, releasing new versions, fixing security issues, making your application/product fit in with the rest et cetera. A good moment to show HN is, I guess, the moment where your potential users can really see what your app will be like when it's near completion, in a way that they will share it with others. And about your "product": good luck!