SSN procedure (NYC)

Hello everyone.. sorry for this spamming the sub again with a question… when can we apply for SSN? I went to the website and started looking for slots it was available.. it does show up… should i take a slot now for a few days after my arrival or wait upto 11 days to book? What is the 11 day thing btw? Someone told to wait till 11 days. Feeling confused! 😕