From San Francisco to Fort Bragg all the way on Hwy. 1 is at least 4-1/2 hours with no stops. If you need more time for stops, etc. consider an overnight in Gualala, which is a sort of an art colony, with an arts center to see the local stuff, and it is charming. It is sort of dominated by Sea Ranch, a development of clusters of rigidly controlled design houses. But it is not intrusive, as they sit like Sonoma County chicken houses in grand isolation on the bluffs.
That aside, I would say if you have two days to make it, you would be advised to stop about here so that the next day you can fully explore the redwood country.