I know that Canie will correct me on this one :) But for sake of argument, indeed most larger CA quakes in the past century have been in the sunrise/sunset times.

Northridge (430AM)
San Fernando 1971 (6AM)
Long Beach 1933 (5 something pm)
Whittier 1987 (745A)
Landers (5 someting AM)
Big Bear (8A)
Hector Mine (2A)
Loma Prieta (5pm)
San Francisco 1906 (5AM)
Owens Valley 1872 (early morning)
1857 LA quake (8AM)
1952 Tehachapi (5AM)

If you look at MOST of the moderate bay area quakes of 4+ they have occured in this time frame as well. I know the Napa quake of 7 years ago was early early morning. 1868 Hayward quake early too? 1985 Morgan hill was morning but before noon. Last weeks 4.2 was 8 at night. So yeah it does appear that between 12 noon at 5pm there are very few if any sizeable CA quakes that have occured between those times.