In another thread we were talking about the organization "Paws with a Cause," based in Michigan, which trains dogs to be hearing ear dogs. It takes about 1 1/2 to 2 years to train a dog to the appropriate level. The first part of the training is standard obedience, done by individual foster-families. After the dog completes that part of the training, it goes back to their headquarters for the specialized training. '
(Hearing assistance is only one thing the organization does; they also train dogs to assist people in wheelchairs and other types of assistance.)
Once they start the hearing-assistance training, they do basic things like train the dog to go get the person if it hears a doorbell, a ringing phone, the "beep" of a microwave, an alarm clock, and other things. At this point it begins to be specialized depending on the person's needs. A young mother might want the dog to react to hearing a baby cry, in person or on the baby monitor. An older person in a wheelchair might need the dog to bring things (like a ringing cellphone) as well as react to the sound.
It's a fascinating process. Exactly how long the specialized training lasts depends on the situation and how much it has to learn.
Generally a person has to wait a while before a dog is ready for him. Once in a while there are situations where a dog is placed and then doesn't work out with the person, for whatever reason, and then it's returned and could be placed elsewhere fairly quickly. But usually there is a wait.
Plus, they will not place a dog if you already have a dog under 10 years old, nor will they train your own dog.