Anywhere from a few days, if the egg is eliminated, to 9 months where the egg would have turned into a baby.
A non fertilized egg will last for about 12 to 24 hours before it begins to disintegrate.
One Week
The egg is available for 24 hours.
Usually about 28 days, sometimes it will come early or if you are stressed and sometimes for no reason at all. If it is very late then it may be a good idea to speak to your doctor.