They can be out of the water for long periods, days even. Most of the time when they require dry-docking, they are back into water once or twice a day for them to rehydrate and eat.
If the injury is only a flesh wound, usually dry docking is all that is required. However, if it does not look like it is scarring up to heal of it is spreading/looking infected, then you should be consulting a vet. A little bit of betadine/water should be ok... maybe use a cotton ball instead of toothbrush.