The Dec 5 date would only apply to areas that received the letter saying that was the date the analog channels go away. In this case, this applies to the San Carlos/Redwood City and possibly adjoining areas. I don't know what the time-frame would be where you are. In any case, by "going away" I just mean "switching over to a static slate message". Going away for real comes at some later, unknown date.
As far as I know, all the analog channels that have been replaced by a slate in other areas are still showing the slate. Does anyone have evidence of any previously analog channels actually being recycled for other uses? Or are they all still carrying the slate? I would imagine this must be the case for you guys in Santa Clara and Mountain View that just got some new channels. Does anyone know if any area has completed the process and even the analog slates are gone?
I don't think a channel scan will go any faster after the analogs are gone. Your TV doesn't know they are gone so will look for them anyway, and on every channel it checks it may take it longer to convince itself that there is no analog signal than for it to detect an active one. So, it may go slower.