I did that last year for the Wine Country. I used the cut off time and projected min avg pace with no adjustments for slower or faster sections, just the avg all the way through. When I hit Monte Rio (is that the right name?), I had the hardest part behind me and was ahead of schedule. HUGE mental boost.
What I didn't add in were the time delays to cross traffic in a few places. You shouldn't have that problem on the Davis route. Quite the contrary.