Frozen Milk

I am going back to work Wednesday. I am gong to do my best to always have enough milk thawed however if my LO's caregiver needs to use one of my frozen packets during the day what is the quickest way to defrost and how long can that milk sit in the fridge after thawed before it needs to be discarded? No offense to anyone who Formula feeds but I would like to remain EBF even when I return to work.