They could be early producers, which are great for our short, cool summer season but no tomato is going to be happy planted out when night temperatures are still in the low 40's and upper 30's. And there is still a very real possibility of frost. Generally, it is recommended to hold off planting tomatoes until both soil and night temperatures are at least 50F - Mother's Day is the benchmark, but sometimes that is even a bit premature. If you use a protective method like cloching or Wall'o Water, you can push the planting date up a bit.

I use tunnels- double-walled plastic with ribs that push into the ground, 18" tall and wide. They are 20 ft. long and so I can put them over a whole row of tomatoes. I used to put my tomatoes out on April 15 but found a 30-year weather chart that said there is only a 2-3 degree difference in the lows on April 1 so I tried putting some out then and it worked just as well. I initially tried only early and cold-tolerant tomatoes but in the last few years I planted an assortment of short and long season heirloom and hybrid tomatoes and they all survive and produce sooner than ones set out May 15 or later, considering that I don't have a greenhouse to grow big plants inside, and am limited by what I can grow under lights to about 11-12". I have had tomatoes out in tunnels during frosts and snow and they were unharmed. I tried WOW's and they fell over on me, and being open at the top did not protect the tomatoes as well, and are much more expensive considering the tunnel will protect a whole row.