How long will it take me to run a 5.20 1500m?

I'm a rookie tracklete, and only a freshman. But this last year I've been discovering that I love to run. My current time (with a muscle injury) is 6.32 and I've got a goal to get it down to 5.20 in the next year or so. How long do you think it will take me if I'm willing to work hard? I'm going to base my workouts and diet around this goal so I'm not chugging soda or scarfing down hotdogs. I'm a girl and like I said, a freshmen in high school. I'll be working out for a couple hours a day 6 to 7 days a week and possibly twice a day. So what do you think? Are we talking a year? A couple months? Thanks for your input.