Hello, Breast milk can be stored at room temperature for roughly 4 to 6 hour. While it can be stored in refrigerator for 4 to 5 days depending upon the aseptic condition. In a deep freezer that is -4*c, it can be stored for as long as 6 months. Never thaw or heat breast milk in a microwave. ... Once breast milk is brought to room temperature or warmed after storing in the refrigerator or freezer, it should be used within 2 hours. Never refreeze breast milk once it has been thawed.