Even if the type of person who browses HN religiously is your exact target market, just posting at a bad time or being unlucky enough to post right before other relevant big news comes out is enough to get buried.
This is a good point. My lessons from this are to pick a time when traffic isn't as high so you have a chance of gaining some visibility. Getting on the frontpage during non-peak hours is better than getting on page 2 during peak hours.