According to Johnny Pez's Insanely Complete Fiction List hosted on my site, with permission, Second Foundation started at 316 FE / 12384 GE / 23968 AD. I'm not sure why Johnny and Attila (link posted by sarge_smith) determined different dates. The advantage to Johnny's list is that he lists all the plot points he used at the bottom of the timeline, so there is really no danger of major spoilers. Also, Johnny's list includes all of the expanded universe (Robot City, Robots & Aliens, Caliban, etc) authorized by Asimov and written by other authors shortly before his death.
Asimov states clearly in one of his introductions that he did not originally plan for the Robot & Foundation Universes to be together. I was looking for the reference, but was unable to find it. This Wikipedia article suggests the universes were tied together in Foundation's Edge.
I'd like to note that that the bottom of the repost of Attila's list is the mention of a book called "Psychohistorical Crisis" which does not fit into the Robot & Foundation canon. The book appears to have some good reviews, so I might check it out sometime.