As long as the seed has germinated and the plant is growing, the cool temps are not an issue.
The only thing I've noticed is they grow a bit more slowly with cooler temps but they sure have less pests in the cooler weather. When we get hot & humid I have to patrol constantly for bugs.
Freezing temperatures are another issue. We saw 31 degrees on Friday nite here. I had the maters and cukes covered with sheets and all are just fine.
