Same goes for spending a month finessing your YC application. tptacek's point is that the time spent getting into YC could be better spent building your product.
If the first month is critical, you're probably picking a crappy segment to chase. Yeah, the window's closing on social networks. Go do something else.
Its not the first month thats critical, its the last month. Any plan with an extra month at the end has more chance of success. The problem with a startup is that the total amount of time available is rarely known in advance.
However, you'd be one month behind in development. For a start-up, that could be critical.