How long will it take me to reach my weight loss goals?

I am a 5'6" 180lbs 21 year old female in mostly good health. I started working on my weight 2 weeks ago at 190lbs. I am under the supervision of a physician who has me eating 1200 calories a day, with 5 meals a day between 200-300 calories. That caloric intake will decrease in about 2 weeks. He has me taking in about 90g carbs and 90g protein with under 25g of fat. I eat a lot of whole grains, vegetables, fruit, beans, nuts, and low fat dairy products. I also drink about 90oz of water daily. He doesn't want me doing any extreme exercise yet, but I do at least 30 min of cardio daily and 15-30 min of weight training or calisthenics. That amount of exercise will be increased in a few weeks as long as he gives me the ok, (he wants to regulate my blood sugar with diet first to make sure I'm not burning muscle). I have about 30% body fat and I'm looking to get that as low as possible. My goal weight is about 125lbs, I'm ok with ending at a higher weight as long as my muscle mass increases. I'm looking at a time frame of about 6 months, if I continue to lose 2.5-3lbs per week. However, I'd like some input from other people who have lost over 50lbs. How long will it realistically take me to reach my goal? How long did it take you?