dear lord spandex
regarding your post concerning radar release.
if you were at an uncontrolled airport and it was VFR conditions and did not have overlying class B airspace you could takeoff without a radar release.
But if you were at DCA, you would need a clearance to enter class B airspace. if conditions were IFR you would need a clearance.
if dca tower were closed and you could get hold of tracon and IF they would release you, yes you could takeoff.
Chances are tracon would have you wait safely on the ground till things were sorted out. SINCE tracon had not released anyone from DCA for departure, (along with noise curfew) there wouldn't be departing traffic for the inbound traffic to worry about.
You mention to bubbers the possibility of a plane being on the runway while another attempted to land. Quite possible, EVEN WHEN CONTROLERS ARE AWAKE.
see bubbers comment about landline and block of time.
ditchdigger...for the purpose of the discussion time of day would be unimportant.