Does this piece of ground stay saturated after such a rain normally ?? If it drains pretty well normally, I wouldn't think it will be a problem. My camp has clayish soil and I put a couple shovels of aged mushroom compost in the planting holes along with native soil. I usually put 5 gallons of water on each tree at planting, and we've had heavy rains a day or 2 after planting - never a problem for us. We never lost a tree.
One way to help with preventing the " clay basin " effect is to score the side of the planting holes with a hand-held garden " hook " - the kind with 3 or 4 tines on it. I also use that tool to punch some holes in the sides of the planting hole to help roots expand out of the hole.