After three days of soaking the wood I got impatient and added it to the tank while it still floated. The tannins had stopped leeching as the water it was in remained clear, so i went ahead. Held it down by placing two heavy rocks on top and let it soak in the aquarium. I really wanted to see it in place.
The other main reason I added the wood so hastily was the plants I bought couldn’t be added without it, as they needed to go around the wood. I had the plants in a bowl of water floating but they needed to be in the aquarium.
Getting the plants to anchor in the substrate was a chore, and even now the odd one or two dislodge and float to the surface but the roots are anchoring and they look really nice.
My tank is now really heavily planted, but with plants there are no real disadvantages. They improve water quality and are great for all the fish to swim around and hide in, and they look great.