2020 for China to have 3 carrier strike groups is doable. The third carrier still be conventional powered but with catapult.
I do not think so.
The 2nd carrier may launch in 2017...it will then have to be completely outfitted...which will take another year. it will then have to go through its trials, which will take another year.
It may be commissioned sometime in 2019...but then, it will take another almost two years before it become fully operational. That would be a second operational carrier by 2021.
The 3rd carrier we have not seen yet. It is going to be a different beast. The first true Chinese indigenous design from the keel up.
First steel cut may or may not have happened. But once they start actually work on that carrier, you can figure probably at least three years until launch (most take four), another year to year and a half to outfit, another year to year and a half for trials.
This would mean it will be probably 2021-2022 before it is commissioned at the very earliest. Another two years for that one to be operational. Perhaps by 2023-2024 at the earliest, the PLAN will have three fully operational carriers.
We shall see if they do so because...time will tell.
But IMHO, NO WAY do they have three operational carriers by 2020...or for that matter, even three commissioned by 2020.
They may have two commissioned by 2020, but that is different than even having two operational by 2020.