The trip back from Century City at 6 or 6:30 PM will be long, can easily be 1 1/2 hours.
You might look for alternate routes, like taking Topanga Canyon to PCH, and then taking Sunset into Century City.
On Way back in the evening it is a bumper to bumper on 405 & 101 no matter where you come from. Best leave at 4 the latest wherever you are or after 7 PM
Hope this helps!