It really depends on how torn up the fins are. If it's just a small nip it may heal in just a few days. The closer the nip is to the fishes body the longer it will take to heal.
I suggest adding Vita Chem for additional vitamins. Garlic Guard or even garlic juice from the grocery store (link below) added onto the fish food to boost the immune system. Keep the water as pristine as possible.
The color may never return to the fins even after they're healed. All seven of my gold barbs were really nipped when I got them, some with no more than a nub for a tail. After about a week everyone's fins looked smooth and fin-shaped but even now, probably three weeks later, the beautiful red color has not returned to the new fin growth. I hope it will but I kinda think it won't, which is ashame because they're an amazing color.