No answer to this will fit every dog. Some dogs may need a few minutes several times per day, some dogs a few minutes every few days. But we are continually interacting with our dog which can be used as a training session that doesn’t take any time at all. For instance, recall training. You call your dog by using their name several times per day. Why not carry some treats with you, call your dog using your recall cue, and reward them when they come to you, in doing this you are training your dog to recall without actually a training session is. Your dog will learn that coming to you is a good thing!
Studies have shown that less is more! The more the dogs in the study were trained, the less they learned.
The important thing is that you understand when to train and when to stop.
Is the environment right for training? Are there too many distractions? Learning happens effectively in isolation, then gradually adding distraction when the initial training has been effective.
Are you motivating your dog? The type of reward you pay can improve training, This isn’t bribary, I have read some trainers describe the use of food as bribary. If you don’t get paid to do the work you do you feel undervalued and less likely to want to do a good job. It’s the same with dog training, The payment they recieve for perfomring a task will determine the results that you will get. For the behaviours that they struggle with, such as loose lead and recall, increasing the value of the reward will result in effective learning.
Are you both in the right place to learn? Are you tired or annoyed, have you had a good day? Training when you are tired or stressed can be a disadvantage, Is your dog tired? You may find that they show some disengagement or avoidance behaviours. This is communication that they don’t want to engage in learning so stop. If you see your dog avoid training by sniffing, acting foolish, scratching, yawning etc stop. let them rest.
Rule of thumb is less is more. 5 minutes is better than 1 hour. Reward for great behaviour that are made during the day,