They have shorter shelf life than many seeds. The time frame probably varies a bit by species, but I would say they all should be sown within a year of harvest.
You are down in zone 8 so you can. They germinate in cool temps 60-65, and since they are quite cold hardy, they can be planted out in your area after they get a few true leaves to bloom come spring.
Remy

I'm not sure about pansies, but violas last 2-3 years when stored properly. Starting time? I defer to Remy~~

We have run into the common name problem :) Pansies are violas. In referring to the shorter shelf life, I was commenting on pansies.
Remy