What is considered to long to be under anesthesia?

Dear Ms. Cmvilla45,
Thank you for your questions.
Simply stated the length of anesthesia is only one of the factors related to a safe surgical experience. It's not unheard of having anesthesia greater than 24 hours (detox patients, head injury, separation of conjoined twins, major reconstruction, etc)!
General anesthesia can be compared to flying in a commercial airliner: the most risk is the take off and landing not the absolute time of flight.  A 2 hour flight can be very dangerous in bad weather as can a 2 hour surgery in a unhealthy patient or with major blood loss.  Conversely, with a well trained and experienced pilot (Anesthiologist) in a well maintained plane (certified surgical center), monitoring the plane and weather conditions (Anestheologist monitoring the vital signs, blood loss, etc) 6-10 hour flight in clear weather  (healthy patient and standard procedures followed) is extremely safe.
However, in general for elective Cosmetic Plastic Surgery most Plastic Surgeons try to limit the surgical time to approximately 6 hours.
There are four main groups of complications that can occur with any surgery1) bleeding= stop all aspirin and NSAIDS (ibuprofen, Alleve , etc 2 weeks prior to surgery)2) infection= take antibiotics as directed3) anesthesia= local vs general 4) inherent risks= scars, irregularities, secondary surgery and rarely ultimate compilation of death 
Nothing substitutes for a personal evaluation, a review of your medical history/medications and a face to face discussion of your options, goals and desires.  Realistic expectations and clear understandings of what will be done and in what ordershould be agreed upon in the event that the the procedure time should need be shortened.
Ask your chosen Plastic Surgeon:1) are his/her Anestheologist Bd. Cert.?2) does he/she work in a fully accredited Surgical Center?3) what arrangements have been made if a transfer from the surgery center to a hospital if necessary?4) how far away is the surgery center away from the hospital with a transfer agreement? 
I recommend that you schedule several consultative appointments with Plastic Surgeons who are experienced and Certified by the American Board of Plastic Surgery. In addition ideally a members  of the American Society for Aesthetic Plastic Surgery (denoting by membership as having met additional criteria and a focus on Cosmetic Plastic Surgery).
I wish you my best and success,
R. A. Hardesty, MD, FACSDiplomate and Certified by the Am. Bd. of Plastic Surgerywwwimagineplasticsurgery.com4646 Brockton AveRiverside, Ca 92506(951) 686-7600

Obviously the shorter the time, the better and articles will talk about 5-6 hours as being the cutoff but I've done 7 hours without any adverse problems and I think if the patient is healthy, precautions are taken to prevent blood clots, and the patient is kept warm, 7 hours can be easily tolerated.  But if  you want the safest options, then consider breaking up procedures if it will exceed 6 hours.