Teh FDA will nto announce it before the company. The first you will hear will be (a) a company PR, (b) if there is a leak, the source of the leak, or (c) the FDA is the company doesnot make an annoucmenet within a specified period of time (48 hours? I can't recall). Esssentially, the company is given the opposrtunity to make the anouncement in the way the company thinks best. This is more critical for CRLs or denials, so the company has an opportunity to spin and provide a path forward. Some companies will announce in AH some companies will announce in premarket. TEh stock will usually be halted at the time the annoucnement is made so that the information can filter through the market and allow all traders an equal chance to access eth information and decide how to proceed.
Ocassionally the FDA accidentally leaks approval info (I think the FDA responded to a Gekkowire email re: POZN before POZN had an opportunity to announce), but usually the FDA willnot be the first place to learn of an approval.