Odd title. It's sage advice but I struggle with the inclusion of "last minute". There's nothing "last minute" about this IMO - if you're having to figure any of this out at the last minute, you aren't the YC type, I would guess.
We've decided to enter YC 3 days ago with an new idea. Surely the fact that we have not spent months preparing betas before the YC entry deadline doesn't effect our chances of building a $1B company.
I understand that YC is primarily looking for founders with a good shot at achieving that. I don't think that not having a clear idea of what we want to build yet is as important as our ability to figure that out by talking to customers.
Paul Graham keeps hammering in that a good founding team capable of thinking up good ideas and executing them well is what matters most. So I'm choosing to take that at face value.