You will not formally apply for certification until you have completed and submitted the documents listed on the PAC in FAA Order 8900.1, Figure 2-3-1A of Volume 2, Chapter 3, Section 1. Therefore, you should invest the time and resources in developing the PAC items before you begin your formal application.
At least 45 days prior to the date you wish to schedule your formal application meeting, submit the Formal Application Letter to the Certificate Holding District Office (CHDO) and include at a minimum: