The following applies to dog training: To teach your dog something new or reinforce what it has already learnt, you should train it for around 15 minutes a day. Depending on your dog's age and attention span, you should break up this training session with breaks. Puppies in particular have a strong play instinct, so you can quickly overtax them with a session that is too long.
It takes a lot of repetitions for a dog to really internalise a command. You can therefore integrate dog training into everyday life and have your dog sit during a walk, for example. Remember to reward him in these cases too when he has performed the command correctly - be it with words, cuddles or treats.