I found the following link very helpful when it came to milk storage and use. http://www.pamf.org/children/newborns/feeding/storing.html
Medela's website also has a lot of helpful information. I personally didn't refrigerate it unless I knew I wasn't going to use it within the next 6-8 hours. It was just easier than going through warming it under the tap. That doesn't exactly answer your question though does it?...After I warmed refrigerated milk, I always tried to use it within 2 hours and I never re-refrigerated it after that. I was concerned that the warming/cooling cycle would damage it...but again, not a solid answer to your question...just what I was comfortable with.
at 8:55 AM on Oct. 13, 2008