Handling BM

Hi mummies, how long can chilled bm once taken out of fridge, last in room temperature? I am suddenly thinking of letting chilled bm sit out within a certain timeframe that it can last before warming it up (warmed bm last at most 2 hrs?) so as to extend the lifespan of the bm instead of wad I do usually, warm up chilled bm directly taken out from fridge which can only last 2 hrs..nowadays it is quite hard to predict my LO's feeding time? sometimes he goes 3 hours, 2.5 hours, 4 hours, 5 hours, 6 hours.