My opponent's Active Pokemon is Eternatus VMAX with the "Eternal Zone" Ability working, and they have 8 Pokemon on their Bench. I use Quaquaval ex's "Exciting Dance" attack, doing damage to Eternatus VMAX and then sending out Ting-Lu ex. Will Ting-Lu ex's "Cursed Land" Ability shut off "Eternal Zone" before the entire effect of "Exciting Dance" completes?

Yes. The switch effect of Quaquaval ex happens, and then with Ting-Lu ex entering the Active Spot, Eternatus VMAX's Ability gets shut off, meaning that player must immediately discard Pokemon until they have 5 Benched Pokemon. Then, Eternatus VMAX switches with a Benched Pokemon.

Relevant cards

SWSH3_117

SV2_52

SV2_127