@Finn dAbuzz,
"What not many know is approximately one hour before these tragic events unfurled, under what appeared to be very normal circumstances, Farook telephoned his mother and asked if she was available to babysit the parties’ six-month old daughter for a few hours. Farook stated he and his wife had a doctor appointment to attend and they did not want to bring the baby with them. Farook’s mother, like any grandmother, was more than happy to oblige and presented at the couple’s residence to watch the child."
http://www.obermayerfamilymatters.com/2015/12/what-happens-to-the-youngest-victim-of-the-san-bernardino-shooting/
ABC News has a timeline which shows Farook entering the banquet event at 9:05 a.m., leaving at 10:37 a.m., and returning at the time of the shooting at 10:58 a.m..
http://abcnews.go.com/US/detailed-san-bernardino-documents-reveal-timeline-shooter-neighbors/story?id=35844401
This suggests that the decision to carry out the attack was made at the last minute, else arrangements for care of the child would have been made in advance, instead of phoned in by Farook at the last moment, about an hour after his arrival at the party. It also suggests that his wife, after handing the child over to the mother, only later joined Farook.
An hour and a half is far longer than necessary to "scout out the scene".
Farook had previously had an argument with one of the attendees, about Israel. Farook is reported to have made a statement that could be construed as a death threat.
http://www1.cbn.com/cbnnews/us/2015/December/Rabbi-San-Bernardino-Terrorist-Targeted-Messianic-Jew/
It has also been widely reported that Farook left the party angry after a verbal altercation.
On the other hand, his wife, Malik, was surfing the Internet looking for information about ISIS, just before 9:00 a.m., while Farook was driving to the conference/banquet. That sounds less like an operative than it does a self-radicalized individual "jihad shopping". It has also been reported that Farook had previously been in contact with Al Nusra, the Al Qaeda affiliated rebel group in Syria, as well as Al Shabab, another Al Qaeda affiliated group in Somalia.
http://touch.latimes.com/#section/-1/article/p2p-85230665/
The timeline also reports that Farook placed an undescribed item on the table after he arrived initially, and that a bag with bombs was later discovered by authorities on "a" table. If the "item" should turn out to be the bag with bombs, that would conclusively suggest that the plan had been decided on prior to the event. But the evidence available through the media is ambiguous.