C.B.
I would contact Le Leche League in your area. There is a web site I used for reference while I breasfed. That site is : www.breastfeeding.com
This is what I know from a handy book I used while nursing, but it should be verified by someone else if you have any doubts. The book is called The Nursing Mother's Problem Solver by Claire Martin. "Unrefrigerated breastmilk will keep at room temperature for 15 hours without spoiling. Frozen breastmilk thawed in the refrigerator must be used within 24 hours. If a baby hasn't finished a bottle of expressed breastmilk, you can use it within 24 hours but after that, it must be thrown out." (233-234)
Also, it's best to store your milk in 2 oz portions. That way you are not really wasting too much. You OB/GYN and/or ped should have a local number for Le Leche League. They are an awesome support system that is free for the community of moms who need breastfeeding information.