How long does breast milk last out of fridge?

Ash

I know that fresh milk lasts 4-6 hrs at room temp.. so say I have a bottle of expressed breast milk in the fridge and want to take it with me on a trip. How long will it last once out of fridge? I cannot find a straight forward answer. Also, would you warm it to room temp before leaving the house? I plan to use it within 2 hours of taking it out