Hello, I'm exclusively pumping too - I usually put it out at room temp / in aircon room and finish within 4 hours (but usually within 2 hours).
While it is to my knowledge that refrigerating breast milk preserves nutrients, I realised that my baby seemed to have a lot more gas, spit up and vomiting when I heated up refrigerated milk - even when I don't go past 24 hours of storage. So I just stopped doing this.
For breast milk left at room temp, I also just make sure to smell if I'm unsure - just in case milk has gone bad then it should smell sour!