6-7 hours under general anesthesia! Is this safe?

It is safe to have a long anaesthetic if necessary.  A typical Rhinoplasty takes about 90 minutes. Even with rib cartilage harvesting yours seems like a very long procedure. Clarify with your surgeon to make sure you have the numbers correct.

6-7 hours under general anesthesia, if you are healthy, is not unusual. Typically, if you have any medical issues, a pre-operative physical would be performed to ensure that general anesthesia is low risk. However, that is alot of operative time for a rhinoplasty with rib graft. There might be something specific about your nose that requires such a long operation but this is very unusual. I hope this information is helpful for you.Stephen Weber MD, FACSDenver Facial Plastic Surgeon

Six to seven hours is not an abnormally long time to be under general anesthesia, but the safety of this depends on your overall health.  Your surgeon and anesthesiologist should evaluate you before your surgery to determine if it is safe for you to undergo the procedure for this length of time or not.