I usually wait until they are at least 4 weeks old to do much of any handling, but at that point it is pretty limited. Once they are about 8 weeks old they are a bit more hardy, should be well established eaters and are more ready for handling. 10 minutes per day is about the maximum at this point as they are still quite jumpy, but with regular handling most will calm down and grow into easily handled adults.

FYI, cresteds are not temperature sex dependent--their sex cannot be controlled by the temperature they are incubated at.