Why do I have a hard time starting my 328xi

The longer the vehicle sits without running, the harder it is to start. After sitting overnight, the first attempt to start it in the morning takes 4 or 5 tries. The engine fires up, sounds normal, then shuts down. Sometimes the starter will keep cranking for a few seconds. I wait a bit, try again, and have to do that 4 or 5 times before it stays running. Runs perfectly after that and starts right up the rest of the day. If I run the engine around 11 PM for a few minutes, it shortens the number of tries in the morning to 2 instead of 5.  Any ideas??