At least for the last six months that I have been here, DCA has usually only had 2-3 slots available per class so they tend to get picked relatively early. Although sometimes there are more slots. For example in my Indoc class there were 6 DCA Airbus available and the last one was picked up by a pilot in his 20's. So you never know. But even if you don't get DCA in class it will easily be available on your first vacancy bid.