Seed maturation and dispersal data for conifers is often anecdotal, as a quick perusal of "Silvics of North America" (Burns & Honkala 1990) indicates. For Redwood (Sequoia sempervirens), Olson et al. (1990) state "Redwood cones are terminal and are 13 to 29 mm (0.5 to 1.1 in) long. They mature in autumn of the first year after flowering and are open from early September until late December. Although cones persist for several months, they open and shed seeds soon after ripening."
In the Santa Cruz Mountains yesterday, Feb 1 2010, seed dispersal occurred after a minor windstorm overnight. Seed density falling in a ca. 1 acre opening in otherwise moderately dense S. sempirvirens canopy was on the order of 250 seeds per sq. meter (the photo is the density on a 1 ft square tile)
Although this report yet another anecdote, this date extends the reported date by about a month, and moreover, suggests to me that dispersal is both a function of maturation sequencing and more strongly, environmental factors (specifically wind).
Burns, Russell M., and Barbara H. Honkala, tech. coords. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods. Agriculture Handbook 654. U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 p.
David F. Olson, Jr., Douglass F. Roy, and Gerald A. Walters. Sequoia sempervirens, in Burns & Honkala 1990