Is a longer laser hair removal session better than a short one?

Thank you for your question, the best results are not determined by the length of the procedure, it is based off the number of treatments done. Diode, alexandrite and yag lasers work best for hair removal. However, as I mentioned before it will take a series of treatments to get the best improvement. Please see an expert for an evaluation. I hope this was helpful. Best, Dr. Emer.

There is no relationship to your results and the time to treat.  The number of times the machine repeats a spot and the size of the spot are the limiting factors.  Both the Gentlelase and Getlemax are effective hair removing lasers.  What is vastly more important is to be evaluated by a physician, preferable a dermatologist or plastic surgeon to access your candidacy for the procedure (skin type, hair color, hair density, hair caliber).  Properly set up both the alexandrite and ndyag wavelenghs are appropriate depending on your skin type.  Laser hair removal is associated with one of the greatest reported malpractice lawsuit incidence, usually due to laser burns, scars and pigment disturbance.  It will cost many many times more to treat a laser complication then to avoid it in the first place.  Sometimes facilities that reduce charges by eliminating a board certified physician evaluation,  in the end may not be the cheapest.  On the flip side is when patients are treated with extremely low settings, it provides a placebo treatment, increases the treatment sessions required and may even, at least in dark skinned patients (those most likely to receive ultra low dose treatments), result in their own set of adverse effects.  During your evaluation you should receive a verbal summary of your candidacy as a patient, warned to never be treated when tan, and given some sense of the anticipated number of treatments for a high percentage (90% or so) hair loss in the various areas you wish treated.  Some anatomic areas may require approximately twice the number of treatments to reach the same long-term percentage hair loss than others.  All this needs to be clearly discussed so you know what to expect.
Lastly, pain can be a limiting factor to how large an area can be treated at each session.  Using topical numbing creams over large body surface areas can be dangerous and even life threatening.  Both laser wavelengths (alex, ndyag) are painful, even with the DCD (cold air) device on the Candela branded lasers.  
You mentioned removing chest hair.  If you are female and have significant chest chair, your internist, dermatologist or gp will need to evaluate you for a number of hormone issues.  Those with hormone imbalances will not achieve permanent laser hair removal results.  Excellent hair reduction AND a need for continued maintenance treatments are necessary in those with hormone issues.
Best regards,
Dr. Christopher  Dannaker, FAAD
Fellow, American Academy of Dermatology
Certified, American Boards of Dermatology and Preventive Medicine