It seems pretty clear that he was still at the AP offices at 3:15PM: https://twitter.com/JoeBelBruno/status/441713742955307008
This tweet indicates Dorian had left the AP building by 4:11 PM: https://twitter.com/byandreachang/status/441727789629067264
The P2P foundation post showed up a bit before 5:27PM Pacific Time. The Reddit thread was posted at 5:27PM: http://www.reddit.com/r/Bitcoin/comments/1zrshb/real_satoshi_nakamoto_denies_being_dorian_nakamoto/
Driving time from AP's downtown offices to Temple City is around 20 minutes without traffic; At around 4PM, it's possible the trip would have taken a while longer with traffic. Even so, there's enough time for him to have gotten home and make the P2P foundation post.
I'm digging for more timestamped data points to establish how early he could have left the AP offices, and when he might have arrived back at home. I'll update accordingly.
I donno. I doubt even if he did get home in time, posting would have been not a top concern of his. Securing his stash would have been.