Since I have three dozen plants growing from seed collected from 2005 Hibiscus moscheutos, I know know that a longer & hotter growing season allows the flower to set mature seed by the end of October if there hasn't been a cruel hard frost by then!
I soaked seed in water on a shelf in the kitchen window in February. After severl weeks sprouts started sporadicaly. Pluck out & plant into soiless mix cell packs or pots & put in plastic bags under lights.
I've not tried the winter sown method with this species. Perhaps I'll try this this winter!
Good Luck
sam

Thank you Sam.
I appreciate that very much.
Hala.