Many people think it's necessary to soak split peas overnight before cooking them, but it's not imperative.  Soaking peas shorten their cooking time to about 40 minutes instead of 1 to 2 hours (depending on the brand you buy).  You can do this if you want to cut down the cooking time, but in my opinion, this will cut down on flavor, as simmering the soup as long as possible with the bone adds so much more flavor.