That will depend on your treatment for your eye allergy. If you do not do anything, it may last longer than you expect. For curing eye allergy, you can take eye drops to reducer eye allergy. Just go to drug store and tell them your problems and then they will help you find the suitable eye drops. do not rub your eyes. Make sure your hands are clean. If things get worse, you are recommended to have a check by an eye doctor.
It depends on the order of severity of your allergic eyes and your treatment. Usually the not-too-serious eye allergy will get recovery for a week by keeping on using the eye drops that the doctor suggests. However, if you don't accept the treatment, the eyes may get worse. Thus, you'd better positively treat the eyes with medicine or the eye drops.