I expect these young gymnasts in China are doing up to 10min handstands in training. (The coach said they no longer do 30min handstands.)

That’s still far too long. Training muscular endurance of that duration will not help them in Artistic gymnastics. Except — perhaps — in terms of psychological toughness.
Note that the Chinese coaches do the handstands on a bar. That’s much safer on the wrist.
