Hi Justin,
For me personally I had to do a 6 month medically supervised diet and exercise program per my insurance (Cigna). I did mine through my surgeon's office but others have done their's through a Primary Care Physician. For mine I went to a group meeting once a month at my surgeon's office. They would record my weight then we would have a class on a nutrition topic (reading food lables, importance of exercise, healthy options for eating out). Some in the class also had a weight loss goal set for them by their surgeon that they had to meet before the end of the 6 months, my surgeon did not have this requirement. At the end of the 6 months I had to get all my pre-op testing done so my PCP would write me a medical clearance for surgery. Not everyone's PCP made them do this. Some didn't do their testing until they received insurance approval. The testing included blood work, chest xrays, Upper GI and gallbladder ultrasound. Once that was done, my clearance letter written, the surgeon's office submitted all my paperwork to the insurance company for approval. I received an approval in a few days and my surgery was scheduled for the next month. From start to finish this process took me 8 months and I have my surgery on March 16th. Since you only have to do a 3 month supervised diet yours may take a much shorter amount of time. But I would plan on it being at least 5 months before your actual surgery date.
As for the psych eval, mine was very quick. It was a 30 minute session with a psychologist. She asked me questions about myself, what I do for a living, how long I have considered weight loss surgery, what else I have tried, why did I decided to do it now, have a researched the surgery. She also asked me questions about my history with weight, was I over weight as a child, what are/were my exercise habits. Then she asked if I had told anyone about wanting surgery and if they were supportive. Basically to me it seemed like they were trying to make sure I was aware this is a life changing decision, that I wasn't making an impulse decision to have it done and that I have a good support system in place after surgery. It's really not that bad at all.
Like you I was really upset when I found out I had to wait so long for the surgery. Once I decided this was right for me I wanted to have it done tomorrow! Looking back though and seeing how much I have learned over the past 8 months I am grateful to have had the time to prepare myself for this new lifestyle. I hope that helped to answer some of your questions. Good luck!