The quick answer? Immediately! But it's not what you think.
Training your dog is not just getting your dog to sit. When I talk about training, I am talking about your day to day interactions with your dog.
As soon as you bring a dog into your home, you need to lay out the rules. If you don't, they have no idea what is expected of them. If you aren't clear about what is right and wrong, you set your dog up to fail. And in turn you get frustrated because your dog is being a "bad dog", when in their mind they are just doing normal dog things like chewing, barking, etc.
The behaviors that you allow to happen become a habit. So if you don't like that behavior, don't allow it to continue. How do you stop the behavior? It depends on the situation and the dog. This is where enlisting the help of a professional dog trainer comes in handy. A trainer can show you different ways to interrupt the behavior, redirect their attention, or give them an alternative behavior to do.
Some ways to start training right away:
1. Show your dog where you would like them to eliminate. This should be the spot where you would ultimately like them to go. Do not start with potty pads, then have them go on the patio, and then later on go in the backyard. You will confuse your dog if you keep switching where the toilet is, and this will lead to more accidents. Have a cue such as "go potty" so they know when you want them to go. Praise and treat your dog as soon as they finish eliminating.
2. Expect manners before proceeding to do something with your dog. An example of this is putting on the leash for a walk. Many dogs lose their minds to go for a walk, but don't put the leash on a crazy dog. Wait for the dog to be calm and behaved before clipping the leash on. This goes for leaving the house too. Don't let your dog burst through the front door, wait for some self control before releasing them to go outside.
3. Don't give into your dog's demands. If your dog is whining and scratching at you while you eat dinner, don't cave and feed or pet your dog. I don't even want to you to acknowledge your dog if they do this. Eyes up, mouth closed, and ignore! Be patient and wait it out. Your dog will eventually give up and walk away. When they do, you can praise (don't treat) them for being good.
There are many more ways to get started with training your dog! If you want assistance during this process, feel free to email me at firstname.lastname@example.org and I will be happy to answer any questions or get you started with a training regimen.