Planting out seedlings (mostly annual flowers)

Hullo gardeners! New (this year) to seed starting and DG, unless lurking for several months counts.

I'm posting, at last, to ask about which sorts of seedlings can be planted out before frosts are over. Finding this information is tough by searching, whether here or more widely.... I have the hazy sense that species that are frost-tolerant on the other end (when full-grown in the fall) aren't necessarily ready to face a late spring frost (makes sense, since THEY'RE BABIES).

But indoor-light space is tight...and my yard is a zone 6b eastern Massachusetts wasteland....and surely some of these sprouts would love to be out there despite the "low of 34" forecast for a couple of nights this week. I've started hardening off many of the seedlings, apart from those (heat-loving vines) that I know can't go till late May. But for actual planting, does anyone know about

Stocks?
Snapdragons?
Globe amaranths?
Salvia?
Impatiens?
Alyssum? (ready to experiment with some of those)
Cosmos? ( a few of those are out already)
Windowbox (annual) lobelia?

perennials also: Echinacea (I put three of them out, to see how they do) and hyssop.

Will try to include photos.

Sometimes it depends on the varieties as well as the type of plant. Our Salvia is tender in winter where I am, yet I have seen it gtowing farther north without a hitch. If you harden off, thats good. What we do to get a start on plants is plant out if you know you will have a few days of warmth, cover or protect them from cold and winds but I told my daughter her new plants, seedlings and cuttings would be fine down to 38* with no covering. (In Feb) and everything pulled thru with flying colors and never hiccuped. (Except the sunflowers, darn snails) Good luck!

Snapdragons and Alyssum should be fine. I would guess Cosmos, but I am really not sure. I find snapdragons both overwinter here if it is mild, and reseed a bit, the new ones coming up late winter and shrug off frosts. Alyssum is the same. Cosmos- I have some self seeding, but they do not come up quite so early, so I think they will be find but I am not sure.
Hyssop I would guess should be just fine-it is perenniel for me, and I even had some cuttings I left out in a cold frame all winter-every one rooted out there.

Kittriana and Pistil, thank you so much! Your responses reinforce my hazy ideas about snaps and alyssum, and some confusion over the Salvias. I guess it's just that there are so many of the Salvias. I had a white Salvia last year--much loved by the bees--that hung on in the fall, so I brought it in to the enclosed porch, cut it back a couple of weeks ago, and it now seems fine outside again. But the seedlings are shaky ("seascape" and a red Salvia).

Pistil, I guess I should get right down to hardening off the hyssop. Definitely said to be a bee favorite.

Things got really busy this week so I couldn't check back for replies, and in the meantime some field data presented itself:
-The Cosmos and Echinacea seem okay, despite 30-31 degrees one night this week. (They are in a spot right by the house, though.)
-The stock outside in a container seems okay.
-Some snaps in a container outside perished. They were left overnight accidentally...

Today, for the first time this spring, the 7-day weather forecast has nothing lower at night than 40 degrees. Whoohoo!!

I hear ya on the nights at 40*. I have salvia greggi, but Houston is only liveable in when its winter. They throw seeds and return every year. My sages, salvias, a rosemary and the gold is lantana