how long will it take me to lose 25lbs?

I'm 17 and 165lbs (I was 177 but I lost 12lbs) and i'm 5'6". I just got an exercise bike and I plan on using it 5 days a week and for 25 minutes. And I'm going to go for a brisk walk 2 times a week. I also do cardio exercises such as mountain climbers, jumping jacks, sit ups, and I do squats too. I eat pretty healthy (lots of fruit and veggies) and I eat 1200 calories a day and burn about 250 from exercise. How long will it take me to lose this weight?