As soon as it can be demonstrated? What do you think will happen to the party involved in attacking a carrier battle group?
"Welp, they got us. Time to pack it up and go home."
Is this the scenario that plays out in your mind?
Demonstrate:
1
: to show clearly
demonstrate a willingness to cooperate
2 : to prove or make clear by reasoning or evidence
crowded classrooms that demonstrate the need for more schools in the area
3
: to show or prove the value or efficiency of to a prospective buyer
demonstrate a new kitchen gadget
China doesn't have to actually attack and defeat a CBG to demonstrate they they COULD. They can show it against a weaker opponent, say India, should there be a conflict there. Or they can
demonstrate it in their own exercises or in a multinational peaceful exercise/war game. In fact, setting up and participating in regional war games is one of the ways a nation can flex their international might. They can also make low key demonstrations against other vessels that may not get a lot of wide press for the masses, but get noticed by the ones that matter. We see their cyberattacks every day, all across the US and it's allies. These serve to distract and also warn against opposition, not much different than marching an armored column along some contested border.
If the US has ample evidence that a CBG in regional waters would get neutralized, to the tune of TENS OF BILLIONS of dollars and THOUSANDS of lives, even if not sunk necessarily, but scrambled, confused, and disabled, it would be a very strong deterrent to any Chinese ambitions.
Drone swarms, hypersonic missiles, satellite control, cyber attacks; these are the modern equivalents of carriers, aircraft, and subs in WW2 against battleships, cargo vessels, and legacy power relics from WW1. The balance of power is shifting underfoot. Could China resist all 11 US CBGs? Probably not, even if they could/would all get sent to that region. But would the american populace endure the loss of even ONE? China is making very sure the answer to that is.....
NO, via constant social media based moral attacks.