Doctors' philosophy on this vary from a few weeks to never again depending upon their experiences. The basic issues are:
Healing - alcohol is somewhat corrosive to the stomach lining so one needs to give things a chance to heal first,
Alcohol tolerance - rapid stomach emptying means it tends to hit faster, and with less (i.e., a "cheap drunk") so care must be taken there,
Transfer addiction - we can no longer satisfy whatever addictive tendencies we have with food, so it is easy for transfer that addiction to something else, like alcohol, drugs, shopping, gambling, etc. What was a casual habit of a glass of wine with dinner occasionally can easily turn into full blown alcoholism.
Liver health - starting as morbidly obese, or worse, our livers are not usually in very good shape to begin with (hence the "liver shrinking" pre-op diets that are often prescribed) and the liver is further stressed from its role in metabolizing all that fat that we are rapidly losing. It doesn't need any more stress from ingesting a known liver toxin like alcohol (not a judgemental thing, just our physiology at work).
My surgeon is also a biliopancreatic (livers and pancreas) transplant surgeon, so he is in the no alcohol as long as we are losing weight camp (and ideally forever) and indeed we sign a contract to that effect - he doesn't want any of his bariatric patients coming back onto his transplant table!
Those are the issues in play, and some aspects bother different surgeons to different degrees, so they have different policies. Check with what your surgeon's policy is, and decide for yourself - we are all adults here.