There are plenty of ways to do legal back-breast turns in your i.m. The key is finding one that works best for you.
Whatever type of turn you use (open, back flip, or crossover), you must not roll past vertical before touching the wall with your hand.
Also, no matter how quickly you turn, not doing a good pull-out negates any advantage you gained. Do great pull-outs on all breaststroke starts and turns!
If you're not comfortable with the flip or crossover, do a quick open turn (while getting a good breath) and follow it up with a long streamline before your pull-out.
Here's a crossover turn that pushes the limit of the rule. He's backstroker Adam Mania, of Schroeder YMCA in Brown Deer, Wisconsin (near Milwaukee).