How long do approvals last

Hi - I was approved in August through Amerihealth for a lap rny.  Just wondering if there is a time limit for the surgery as I have no idea when I'll be getting a surgery date. My bmi is 41, comorbidities of severe arthritis of back and knees, sleep apnea, hiatal hernia, high cholesterol, family history of heart disease.  Thanks for any info! Deb