The chips design is pretty much done and dusted at this point for the most part. Just some Q's and T's that need to be done... They do need to do additional QC testing and ramp up production and stockpile components and build out the software ecosystem and work with developers.
It's done indeed, but it's not available to mass produce until Q3 2020.
Well Microsoft will have benefit from early release no doubt, but it will make all Xbox One X adopter disappointed, also if Microsoft using AMD Navi 20 lite and Zen 2 as well, they will comes at the same time frame as PS5. Navi 10 itself will probably going to be release on the summer and Navi 20 next year.
PS5 will probably will have navi 20 lite along with Xbox Next , so probably we will ended up seeing the same pattern like with PS4 and Xbox One when it was released.