Depending on where you live, I usually plant all of my seeds in Spring. Farther North, definitely, Spring.
What zone are you in? See if this helps you.
Sometimes it is better to plant perennial seeds in the fall because most need a cold period to make the seed viable. When spring comes your seeds are already in the ground and in a moist condition ready for the soil to warm up. I plant all my cone flower seeds in the fall.