When does 2020 headcount open up, when does hiring process start ?

I am actively starting my job search, and trying to time it in line with 2020 hiring. Ideally I plan to join a company in January. Hence the questions: 1) When does 2020 headcount open up? When are the jobs posted ? Will it be later this year ? Or early next ? Or is the headcount rolling for Google/Amazon/Linkedin ? 2) Depending on the answer to (1), Am I at a disadvantage if I start applying now ? Would I be able to have better chances due to many more openings if I start in January ? YOE:12 TC:200K