This is a tough question. When is the time right can be relative. The problem with having a dog who is exhibiting behavior problems lies in the fact that most will continue while some get worse :-( All dog owners have put up with annoying behaviors. They can be frustrating which doesn't help with the relationship between Man/Woman & Dog. When we identify a behavior problem in our pet we really have 2 choices we can make.
Either we use Maintenance of the problem e.g. leash aggression (reactivity)- cross the street and avoid the other dog or person -OR- Fix the problem through applying behavior modification techniques that can be taught and applied more easily. I believe owners should initiate help when their dog's behavior drives them to a point where it is disrupting the calm environment of the home or the walks in the neighborhood that are supposed to be relaxing times for owner & dog to spend some quality time together. Since most bad behaviors can exacerbate, action versus inaction would be most appropriate. Fortunately for all of us, most poor dog behaviors can be improved, including aggressive ones, through professional teachings of behavior modification. Positive reinforcement is rewarding to the Owner-pet relationship and can be a lot of fun. To properly rehabilitate difficult dog behavior it takes a trained eye to identify triggers, apply necessary changes and a lot of patience to bring welcomed change in a dog's behavior. It is never too late to bring about positive change!