You will apply for the CSQ once you receive the AOR2 letter (confirmation that your file has been transferred over to the respective visa office). It will be written in the letter that you should apply for the certificat de selection du Quebec. This should not delay your application, as it happens in parallel to your file being processed by the visa office and is being handled by the Quebec government. In my case, waiting for the CSQ took a total of 3 weeks, and the Quebec govt. sent the certificate directly to CIC.