I tend to sow most fully hardy species as soon as the seed is shed, both in case they need some summer ripening/winter chill regime to break dormancy and also to get them in as fresh as possible. A lot of my species are a bit obscure to say the least, so information on germination can be hard to come by, so I just get them in as soon as they're ready - as of course happens in nature. Unfortunately this doesn't always work.
I've had to invest in a treatment for Pythium (damping off) for the first time this year, possibly because of the mild damp autumn. Some Penstemon and Asclepias suffered particularly badly when they germinated in October. I think in previous years I've sown these summer rainfall species in mid-winter (when the seed merchant delivered them) so in these cases a winter/spring sowing might be best.
The treatment, by the way, is called Prestop and is itself a fungus (it comes as a yeast-like powder) that colonises the compost, out-competing the Pythium. Seedlings are still emerging and don't appear to be failing now, so fingers crossed. Anyway we'll see how it goes. It's nice not to be using poisons anyway.