If the cabbie dropped off Seligman at 12:42 and drove straight back to the party, it would place him in front of the house about 12:47 (based on Mapquest's 2.08 miles and 5 Minutes). At that time of night there couldn't be much traffic.
As for why the house was empty shortly after that, it has been quoted that there were at most 20 LAX team members there at the start of the party. Surely it dwindled rapidly after at 12:05 after the strippers stopped dancing. Even if it didn't, Seligman and a friend were gone by 12:20 and there were four who got in the cab sometime after 12:47. That leaves 14 tops that also left. You should see my office at 5:00. There are at least 20 people who are blocks away by 5:02.
LOL!