I started my seed Feb. 20 for planting into the patch April 20. You are further south than I am. Chicken (in Florida) started his a couple weeks before I did. If you wait to start your seed in March, planting the patch in May, you may miss some much needed spring showers. I'm just guessing at your weather. I could be way off base. Perhaps you are holding off to catch better curing weather (proper humidity for curing) at harvest time, which is something else to think about in terms of seed starting timing, especially if you don't have frosts to worry about. You have to catch your best curing average humidity.
Start seed (indoors if it is cold) 6-8 weeks before you plan to move them to the patch. I go with 8 weeks just to give me plenty of leeway with the weather and if they do go the full eight weeks, the seedlings are a little stronger, and closer to being past the attractive stage to slugs. I wouldn't go much over 8 weeks, you would just be wasting electricity.