3 min is too long, a 2 minute timer seems more appropriate for such a short duration. I've found I hold off using this power when I could use it just because I don't want to waste such a long recharge (especially against other sci ships). Against borg encounters this power is fairly useful when I actually use it to heal myself the long reuse makes it not practical to rely on. I'd rather have a power that is something I can use all the time instead of just once in a while.
I really think there should be a buff to torpedoes while the ablative shield is up, making it more viable to use. In Voyager, a volley of three transphasic torps while the ablative shielding was up blew up a borg cube. I'm not saying make it that powerful, but a torp damage buff would be in line with cannon and make this power far more useful. At least that would make it worth a 3 min timer.