Limiting waste of breast milk

Elizabeth
I'm having a hard time figuring out the best way to not waste breast milk . Each site says different things ! 
My little guy eats over an hour sometimes - little here little there from a bottle. I've heard you have to toss after an hour of being out ! 
I usually don't warm it up and let it get room temp on its own because I heard it can stay out longer ? 
Help ! How do you feed your little one without wasting milk