You have to complete an ATP Certificate Training Program, pass the written test, complete a ground and flight training program for the type and pass the oral and checkride.
My 727 oral was right at 2 hours, the 744 closer to 4. You have to be able to explain all the switches and lights in the cockpit, limitations, etc. Part of the training program is to get you ready for the oral and checkride, there shouldn't be anything new you haven't seen in training.