These are the CDC's published time limits. They're conservative on purpose — milk can sometimes last longer (especially in a cold fridge), but the CDC numbers are the ones every lactation consultant cites.
Smell + appearance are still your final test. Soured milk smells sharp and tangy — that's bacterial growth and it should go. Slight separation or yellowing is normal.
Source: CDC Human Milk Storage Guidelines (cdc.gov/breastfeeding/recommendations/handling-breastmilk.html).