I do it when the roots start coming out -- not just the first hint, but not wrapping around a ton either, -- but if you have "hot" soil, you may want to be closer to the latter than the previous. A more robust plant is safer for soil loaded with nuites.
The only issue would be if the pot is too larger for the plant. you have to water in a small radius and increase that radius over time as the plant gets larger.
think this should cover most bases..