Departure time is push back time. The calculation for estimate time required for taxi out, take off, cruise, desent and approach as well as landing and taxi to the gate that is the arrival time. The time table gives you a departure time and a arrival time what includes all the above named phases of the operation. If you have a usually congested ramp/taxiway then there is a longer time in the time table considert as the actual average flight times
for that particular route.
NG