They don't care about arrival time, just the day. So many flights arrive late (and some early) that they really don't even bother with it.
As for depature time: they will look up your departure time and fill it in for you (as long as the flight numbers are correct) a day before departure, when scheduling your DME pickup. They wait until then because of so many last minute flight schedule changes. If you don't get the DME departure packet the day before you leave, then call.