Hagen Fluval Sea Epoxy Stick for Aquarium, 4-Ounce

I have a concrete feature. i need to alter the shape slightly. can i model this into the shape i need on the concrete? it will need to cure with fish.

Would this work on in water driftwood? Want to attach stones to some wood to stop it from turning.

Would this work for adhering my suction cups of my heaters to my plastic pond liner?

Is this instant hold? Or must I support each piece until it cures?