When do your soil temps reach 60 degrees F and continue rising? When do the ambient air temps remain above 70 degrees F? Then of course you may have a micro-climate that permits an earlier planting date. Those are the dates I would be looking to transplant to the soil. You could start the seeds 6 to 8 weeks before that time if you don't mind potting on as the seedlings grow.

You can plant them anytime. I've started them indoors around December, and by late February or early March they go outside. I also get seedlings popping up all by themselves at any given time of the year. I have to go around and pick them from the flower beds. If you want them to grow fast, i would put them in the ground as soon as possible. They are EXTREMELY fast growers and you can get large plants within a month or two.