Unless you are in the Pacific Northwest, Those are not suited for Z8b. They are long day onions. In Z8b deep south USA, short day onions are seeded in September - October.

I am in Washington State. Just about 45 minutes north of the 45o parallel.

I have no experience in your climate. The Pacific Norhtwest Gardening specifies " as soon as the ground can be worked" which means as soon as it dries out a bit after the spring thaw.

Here is a link that might be useful: Pacific Northwest onions

Awesome. Thanks for the link. I learned a lot from it.

Anyone with experience, ever tried overwintering any of these onions?

I'm in NW Oregon so a fairly similar climate to yours.
I start seeding my summer onions feb. 1st in the hoop house.

Trust me on this one, it's coming from 16 years experience growing onions (and other veg) for my living. If you want to overwinter onions, stick with those developed and tested for it.
Long day onions will all most likely bolt on the second year. Thats a lot of energy to keep them weeded all winter and spring just to harvest a green onion.

Even on good years, lots of my overwinters bolt due to conditions beyond my control. My Walla's almost all went to crap this year. Probably due to the warm spell last month.

defigart. Osborne seed trials in Skagit County and reports good results over wintering Desert Sunrise.
"Overwintering Onions- a new red!
Pretty soon it will be time to plant your overwintering onions. We planted last year at the end of August, and could have been harvesting from late May into July. We took a hard look at our trial at the end of June, and one new variety stood out to us- Desert Sunrise.

At least a 2 1/2 in diameter, Desert Sunrise's flat globe shape makes it look like a big chippolini type. Purplish red outside, good interior, mostly white.

No bolters. Shorter foliage."

Here is a link that might be useful: osborne variety trials

Desert sunrise did very well for me this year. I wouldn't say 'no bolters' but it was only about 5% or so, which isn't bad out of about 700.
It's not the largest onion, but it's the only red that's overwintered well for me so far. Not nearly as nice as 'Redwing' in the fall, but really a great onion for fresh market this time of year.

I ordered some Desert Sunrise, Hi Kepper and Walla Wallas for overwintering. I plan to grow about 100 - 150 of each.

So now back to my original question only slightly modified. When should I start the seed? It appears that these should be planted in the ground around September. (Correct me on that if I am wrong)

I am planting some at harvest in July & some in the Fall.

Here is a link that might be useful: Fall onions

Seed them mid August into flats. Or a little earlier if direct seeding.