How long will it take to lose 10-15lbs?

I'm 5'3 and 130lbs. How long will it take me to lose 10-15lbs if I eat 1200-1400 calories a day (healthy food, not crap) and exercise for an hour a day. For exercise I either ride my stationary exercise bike or do my gazelle trainer or a half hour of both to get to an hour of cardio. I'm not really that out of shape but I've always been on the chubby side and I'd like to be slimmer for my junior year of high school. I've made this kind of my summer project/goal. Any tips or good diets are welcome too, thanks.