Seeds are pretty smart. They know when it is time to sprout. When the temp and moisture requirements are met THEY COME ALIVE!
For plants that are hardy in your zone, you can put them out pretty much any time. Late fall and early spring are the best time. I am learning that MANY seeds can be sown in the fall for the earliest germination in the spring. I was just at Doc’s house yesterday and self seeded calendula and elecampane are sprouting and growing gangbusters. The calendula and elecampane that I am trying to start now are WAY BEHIND his.
For seeds that are not hardy to our area a mid to late spring sowing are probably best. Either that or try starting some 4-6 weeks earlier in the house. I have been doing this with mixed success, mostly related to low humidity and solar influence in the home. If you can overcome those two shortfalls you should have good success.