There's lots of information available about how long pumped breast milk can be kept for, generally citing different temperature ranges.

From the CDC (though the samereference is also cited by the Canadian Pediatric Society

It's cited that milk thawed from the freezer should be used within 24 hours in the fridge, or 1 hour at room temperature.

The Mayo Clinic has an article saying "Other studies have shown that refrigeration beyond two days might reduce the bacteria-killing properties of breast milk".

My wife is exclusively pumping, and is always concerned about using milk taken out of the fridge (generally +/-1 day old) within an hour or two. We often talk milk out, only to have baby fall back asleep. Is there a basis to how long fridge-temperature milk (stored at 3 degrees C for a day or two) can be be out of the fridge for?