less than 12 hours-cells will break down in the urine, as well as bacteria setting in and reading of the cells will be distorted -result will show inconclusive for infection. Also how it is contained. If stored in home bottle or jar; should be sterilized and placed in fridge and first morning specimen is best. But get to the lab or doctor as soon as required. Usually doctor's office or hospital gives sterilized container for the specimen to avoid contamination. Follow the instructions they gave you to collect also.
hope this helps.
