There is no time limit on Social Security Disability benefits. Disability benefits will continue as long as you remain disabled. Social Security Administration will periodically review your case to make sure you continue to qualify for benefits. The periodic review will consist of a review of your medical records.
Additionally, if you are still collecting Social Security Disability benefits when you reach retirement age, your benefit amount will not change. The only thing that changes is the category of the benefit. Your disability benefits after retirement age will automatically convert to retirement benefits.