it depends on so many factors that it's impossible to tell - age, gender, metabolic rate, starting BMI, whether or not you lost weight prior to surgery, etc. The only thing you really have control over is how committed you are to your program. I was a slow loser, but I almost never went off my program. I lost all my excess weight, but it took around 20 months.
the only way I know of to increase your metabolism is strength training. Muscles burn more calories than fat, so the more muscular you are, the more calories you'll burn, even when you're sleeping.