The 2P/1P/1K line at LAS - United is // never // long while regular coach can take up to an hour to clear.
Now for D Gate security, show up at least 1 hour prior to departure and you'll be ok... except:
Friday 5A - 9A, 11A - 1P, 7P-9P: security can take up to 30 mins to clear
Sunday 5A to 7P: Security can take up to 2 hours to clear
Otherwise, the D gates are most active from 8A to 11A in terms of security... lately I haven't had to wait more than 15 minutes and i've done about 30 segments out of here so far this year via the D gates...
I've even shown up for a 730P flight to SFO 30 minutes prior and walked right on the plane...
-nate
(Las Vegas local).