I'm in the same area and am looking at 5/15 as the target for planting out. I have a bunch of seedlings that I'm hardening off right now and should be good to go by the end of next week. I've been watching night-time temperatures and they've been pretty steady in the 40-50 F range.

I am zone 5 and I have put them out on May 5 and had a few freezes after that but I cover the plants. it is easy to cover them because they are small. cardboard boxes work perfect on big plants.

however, the plants will grow bigger if you keep bringing them indoors at night. But if you have a 1000 transplants to get outdoors then you need to get started early to get them all in.

Best bring them in at night and put under lights all night
2nd good bring them in at night to keep the roots warm. leave them in the dark
3rd not so good put them out early to face the cutworms and frosts.

today and the last few days and the next few days. I am repotting the plants into 6 inch pots. I bring them in every night. and I give them light as I need for them to grow. I planted the seeds a bit late.

well my Jalapenos are fine they are a good size. the habs need more growing. they are slow. and most of my peppers are habanero.

I usually put out the tomatoes first. they take the cold better. then when the tomatoes are done I put out the peppers. but I am always ready to cover everything if there is a frost possible at night.

I guess it depends on your goals. I am new to this hobby and I believe seeing the difference is better than hearing.

For example, I have bought a few pepper plants from Chiliplants.com ( 4/24 )and started a couple from seed (about april 1st). I left a few purchased outside, Took a few in, As well as Hardening off some plants by leaving them in shade for a few days, then full sunlight but always taking them in by sunset or before. When you see the Yellow Plants that have barely grown compared to the thick rampant growth of the ones hardened off, you'll know what you want to do for next year! Do you want to see how much stress your plant can handle and still yield? do you want the healthiest plants with the most chiles? It's up to you. I look at my hobby growing peppers as a science project so I don't care if a plant dies or does not grow as capable as it should. I am gaining experience and knowledge firsthand. I also respect and can see how someone who loves peppers would not want to waste a whole season on "experimenting" and losing the joy of a harvest! so i think it's up to you, but for the healthiest plants, Wait waaaayy after frosts.

PS Chileplants.com gave me crazy Mites so I have learned firsthand why most start from seed. I have tossed all those plants aside into their own little who cares section. after taking off every single leaf that showed bugs.