If you intend to store the EBM for later use, it is best to refridgerate it asap. Otherwise, it could stand for up to 3hrs. If your baby prefers warm milk, it would be better if you warm it up. My mother in law says that cold milk will cause wind in the baby. I dont't know how true it is. My dear son prefers warm milk so I've always been warming up his milk.
Some websites say that it can stand for 6hrs but that's provided that the temperature is at 26C, which is like an air con room. But for best retention of nutrients and prevention against the milk going bad and thus causing diarrhea in your baby, it's best to consume to EBM asap.