My understanding is that it completely depends on your provider, surgeon, weight, bmi etc
I was on my pre-op diet (slim fast/soups/fruit/veg) for 2 weeks before my op (I had a band fitted). I wasn't given a goal of weight to lose, I was simply told I had to stick to it to shrink my liver. It was quite frustrating not knowing what to aim for, but I was advised that I concentrating on Lbs lossed/gained etc is not in the future for me & therefore, I didn't need to begin my Weight Loss journey by measuring lbs!!
I am sure there will be someone along later able to give you a more definitive answer, but I would suggest that if your surgeon/specialist hasn't give you a target weight, try to concentrate on the bigger picture - though I appreciate this is easier said than done