Whoops-- I hadn't taken the OP's arrival time into consideration. That's a lousy time to drive much of anywhere in the LA metro area! However, if you must... FlyinHawaiian's advice is sound. To get to La Cienega going North:

Exiting the Hertz lot, turn right (W) on Arbor Vitae (BTW you're only allowed to turn right coming out of this lot, IIRC)
Turn right (N) at the light onto Airport Blvd.
Turn right (E) at Manchester (1st major intersection)
Turn left (N) on La Cienega

La Cienega runs right next to the 405, so you'll get to look at all the crazy people in their cars stuck in traffic... Realize, or course, that you'll be dealing with a fair amount yourself (not to mention stoplights), but side streets should be a bit quicker.

Alternatively, bag all this and take PCH out towards Malibu. Find a nice restaurant. Have a good meal, enjoy the ocean at sunset, and don't think about heading in to West Hollywood until 8 or so... Besides, the fun freak show doesn't really start until after dark-- I think they're hanging out @ Venice Beach during the day!