I think it depends largely on your weather. If it stays cooler as you say, they probably will be ok. Days should be long enough going into late July/early August to not affect their growth. I think your biggest problem may be keeping powdery mildew off of them during the warmer, humid summer weather. That can be dealt with in various ways, including, I've been told, by spraying them periodically with whole milk.

I would try it, you wouldn't be out much but a packet or two of seeds.