Toz stepped onto the bridge leading to the brown stone cube. While he walked, he deactivated his mana vision to let it recover, and when he arrived in front of the cube, he conjured a chisel and a hammer of metal. Since they were magic, their effects would be reduced against the anti-magic properties of the stone, and they would also quickly get eroded. But it would still be more efficient than trying to melt the rock again, especially since the effects of the stone were concentrated inward.
Toz also didn't have the patience to wait for the stone to melt. Not to mention how the cats might suffer if they were chained to the floor like he had been and molten rock began dripping on and around them.