Yeah its a tad risky getting a cool season tall fescue blend going that early. It's still a bit early now, but I have found around the middle part of August is less of a problem in general. Almost 2 months past the solstice, but the hot and humid weather can still be a problem. I do it in stages and I need to get going early, as I am in the woods and want all the new grass to get well established before the leaves start coming down. With the lower sun angle half my yard is much more shaded now too, so I start with that side first.