1997 528i doesn't start in cold weather (60F)

I am having a very frustrating problem. My 528i has trouble starting in the mornings and at night. It has never happened in the daytime or early evening. I turn the key and the starter cranks, but the engine doesn't turn over. I try pumping the gas a little and it does not seem to have a consistent effect. Sometimes the car will start after only a few tries and some times I have to give it a rest for 5 or 10 minutes and then, miraculously it starts. Does anyone have any suggestions or experience with this problem?