Marigolds will self sow really quickly and you can extend the season with covers, cloches, coldframes and hothouses ;-}

Some stuff that requires dormancy can be activated either through drying and/or stratifying (apply an artificial winter via refrigerator).

Sometimes hard seeds like sweet pea benefit from scoring the shell after drying to facilitate hydration so your germination period is shortened. Remember soil temperature is a germination key so place your trays accordingly.

I hope this helps you extend your growing season and get better germination and quick turnaround!