Hi!
I'm no expert by any means, but I'll jump in here....
All hosta varieties are different. Some seeds can be ready earlier than others. The earliest I've heard of is 6 weeks, but this year has been strange with all the heat and I had black seeds in dried pods on my Queen of the Seas at about 4 weeks. Are they viable? I don't know yet.
My suggestion is, if you check your gardens frequently so you don't risk pods drying and dropping the seeds in between inspections, to leave the pods on the plants as long as you can. But you want to be sure and pull any before the first frost, as that does seem to hurt them. And yes, sometimes the pods turn brown, and sometimes they don't - again, depending on the variety. I think the general recommendation is at least 8 weeks to be safe. I've also heard that 8 weeks can be too soon for some varieties.
Seeds are viable when you harvest them. I know a number of people who have sown them right away and have success. Most people wait till winter so it gives them some 'gardening' to play with in the middle of winter. The other reason to wait being, that if you start seeds indoors earlier than November or so, they grow so large by the time you can get them outside in the spring, that they can be difficult to accommodate.
Different varieties of hostas have different germination rates, too. For instance, with Frances Williams, you could have a 90-95% germination. Some other hostas are considered nearly sterile and you may get one or none.
Also hosta seeds can take anywhere from 3 days to 30 days to germinate, depending on the variety. When you sow them, just cover very lightly, keep moist (always!!!!) and don't put them under your lights till you see signs of germination - it keeps the algae down. Temperatures ideally are 70-80 degrees. The warmer the temps - the faster the germination, but not more than 80. Depending on the type of lighting you use, the lights should be positioned just above your growing medium - within 2-3 inches of the surface. As the seedlings grow, you can raise the lights accordingly.
If you wait more than 30 days or so from harvesting to start sowing your seeds, they are best stored in the freezer in a dry airtight, non-plastic container. I mean you can put them in a paper envelope or something (so the seeds are in contact only with porous surfaces for airflow), but then you can store a bunch of them in an airtight container of any kind. If they are next to a plastic baggie or something they can retain moisture and rot. Be sure they have dried for a couple weeks perhaps before freezing, though.
Hope this helps...keep the questions coming if you have any! It's loads of fun and can actually be quite addictive.
No, really!
But I'd like to get some practice and maybe some success in the hopes of being more confident at trying other people's seeds this winter as they become available.