Here is the direct link to La Leche League regarding storage guidelines...
http://www.llli.org/FAQ/milkstorage.html
You can click on it or just copy & paste it in the address bar. Pretty much if you pump and are planning on using it that day, it can stay room temp up to 8 hours (preferably not more than 4 though for max freshness). Otherwise you can refrigerate for up to 8 days (preferably up to 72 hours). Here's some info from the site:
How to Warm the Milk:
Frozen milk: thaw in the fridge overnight or under cool running water. Gradually increase the temperature of the water to heat the milk to feeding temperature.
Refrigerated milk: Warm the milk under warm running water for several minutes or immerse the container in a pan of water that has been heated on the stove. Do not heat the milk directly on the stove. Some babies accept milk right from the refrigerator.
Do not bring temperature of milk to boiling point.
Human milk may separate into a milk layer and a cream layer when it is stored. This is normal. Swirl it gently to redistribute the cream before giving it to baby.
Do not use a microwave oven to heat human milk. It may cause the loss of some of the beneficial properties of the milk. Microwaves do not heat liquids evenly and may leave hot spots in the container of milk. This could be dangerous for infants.
I usually thaw my frozen milk in the fridge overnight and then take a tupperware container with me to the restaurant. When he's ready to eat I go to the bathroom and put the bag in the tupperware container and fill it with lukewarm water and gradually make it hotter. I do this just until the milk feels room temp and not chilly (but not warm so that he doesn't only want warm milk!) Then I pour the milk in the bottle, swirl gently, & feed! I also use a bottle that simulates breatst feeding called Breastflow made by The First Years and he loves it as do I! Feel free to call me if you have any questions! ###-###-####.
Take Care, L..