Join Date: Aug 2006
Location: DCA / WAS
Programs: DL 2+ million/PM, YX, Marriott Plt, *wood gold, HHonors, CO Plt, UA, AA EXP, WN, AGR
Posts: 9,386
2:45 should be plenty of time for a US citizen at IAD, even without Global Entry. Assuming, of course, that CBP isn't staging a sequester-related slowdown. If you're changing from UA to DL, though, I wouldn't want to cut it much shorter than your connection time.
You probably won't be able to use PRE coming off the Int'l connection.