If clear whey has formed, there is no milky liquid left, and your curds seem reasonably sized (forming clumps), feel free to start scooping the tofu curds into the press. Otherwise, pour the rest of the mixture into the milky spots, and wait a bit longer. This part is experimental and one of the trickiest parts of tofu-making, depending on the brand of nigari you use, and the concentration of soy solids you managed to get into your soy milk.