Your are right. Milk is
casein based
protein which is digested more slowly. this can be good during the day or at night as it will cause a slower release of
protein into the system feeding the body for longer.
The times i would advise against milk for your portein drinks would be first thing inthemorning as the body has been fasting over night and needs quick ingestion. And straight after a work out as the muscles will be crying out for
protein to help repair the muscles.