Welcome
So if there is anything I've learned from WLS, its that different surgeons and surgery centers do things differently... and I think answers will really vary person by person. But here is my experience:
1) I had to lose 20 lbs before surgery. My surgery center gave me a "suggested diet" list, but it boiled down to 60 grams of protein, 1200 calories a day. I think other people have had to do programs like Medifast or Optifast before hand, which is much more restrictive and medically supervised.
2) My GP send me right over to surgery. I went through two very quickly-- I choose a new one to get my referral and by the time I wanted to move forward in the process, the original one had left. Both doctors referred me to surgery without much discussion.
3) I started in August of 2013. I went to a pre-surgery informational session. Then, I halted the process until early March 2014 because I wanted to be completely sure I was ready. My GP sent the referral to the surgery center, they called me within 24 hours and I went to the second surgery session 2 days later. From there, getting through psych, nutrition and a one-on-one meeting with my surgeon took about a month-- and I had surgery on June 10th. It could have gone faster, but I teach, so getting time off is difficult and I had to wait until summer to have surgery. It can also take longer depending on how fast you can lose weight and how quickly you can schedule appointments. I was told 3 months to a year was common.
The best advice I can give is to ask lots of questions, get a lot of information and make the best choice you can for yourself.