This came from the La Leche League website:
Storage Guidelines
Term Colostrum
(expressed within 6 days of delivery)
kept at room temperature 27-32 C (80.6-89.6 F) - 12 hours
Mature milk
kept at 15 C (59-60 F) - 24 hours
kept at 19-22 C (66-72 F) - 10 hours
kept at 25 C (79 F) - 4-6 hours
refrigerated 0-4 C (32-39 F) - 8 days
Frozen milk
freezer compartment located inside a refrigerator - 2 weeks
separate door refrigerator/freezer - 3 or 4 months (temperature varies because the door opens frequently)
separate deep freeze at constant -19 C (0 F) - 6 months or longer
How to Warm the Milk
Thaw and/or heat under warm, running water; do not bring temperature of milk to boiling point; shake before testing the temperature; do not use a microwave oven to heat human milk.
Thawed Milk
If milk has been frozen and thawed, it can be refrigerated up to 24 hours for later use. It should not be refrozen.
Hope this info helps you. Good luck going back to work!