Carol, I think we all have to learn our local time-to-plant by trial and error.
I keep telling myself to keep records of when I sowed or transplanted, and how that worked, but even when I do write it down, I lose the notes!
You can get advice like "how many weeks before or after average last frost date", but that ignores things like late frosts, early warm spells, length of unsettled spring weather, how soon deadly summer heat is expected, the microclimate in your yard, and what exact varieties you are growing.
The advice that sounds best to me is "sequential plantings" where each crop gets sown several times, two weeks apart. Then you see whether "pushing the season" actually gains you much, and which dates gave the best results last year.
And try a different variety before giving up on a crop for your climate. They vary a lot!
And once you find an OP variety that does pretty well for you, that you like the taste of, start saving seeds from your best and tastiest plants. You'll automatically select for resistance to local pests, diseases and climactic limitations.
