How long does it take to get a backhandspring?

ok, im 13 and ive been going to tumbling class all last year and now this summer. i go for an hour once a week(monday), nd i wanna no how long it will take to master it, cuz i wanna tryout for my schools cheer team. i wanna be like one of the only people to have it, oh! nd my tryouts are in mid-september! thankx! also i have a handstand,roundoff, forword roll, cartwheel,nd almost have a backbend.