While there are many possible answers to this question, most people would agree that the time that dogs require is the most challenging part of owning a dog.
How much time do dogs require?
I recommend that clients start with a minimum of 60 minutes of physical exercise per day as well as 15 to 30 minutes of training or mental stimulation. Besides normal obedience training, mental stimulation could consist of working for food by hiding in Kongs or in various places around the house.
This guideline is just a starting point. One of my Collies wasn't very happy unless he got a 3-hour combination for the first 4 years of his life, my other Collie needed about 60-90 minutes and my Sheltie was closer to two hours. As they got older their requirements dropped. My 10-year-old Sheltie and my remaining 13-year-old Collie require short walks and a little attention every day. They sleep a lot.
If you get your dog as a puppy, those times might not even take into account the critical socialization time necessary to raise a rock-solid, happy older dog. If you fall down in the socialization category, you can expect much more time later on getting your dog comfortable with the world then if you do it right the first time. Or, you might simply avoid taking your dog places because he can't handle it and what fun is it to have a dog that can't be with your friends and family?
I tell my clients that properly socializing a puppy should feel like a second full time job. At the end of the week if you haven't taken your puppy many places, introduced him to dozens of adults, dogs, kids, noises, and other stimuli, you are taking a chance that he won't be the adult dog you were hoping for.
All my aggressive clients started out as young puppies at one point. It is unusual to see a 7-week-old puppy that is extremely aggressive. So, what happened? It is usually a combination of genetics, improper socialization and traumatic experiences. A dog that gets attacked at the dog park might instantly be anxious around dogs. A dog that hasn't been properly exposed to kids as a puppy might bark or bite a child that moves quickly towards him.
Don't fall into the trap of thinking that your nice big backyard is a natural dog park for your dog. He will happily prance around and come inside in a happy stupor and sleep all night. Dogs don't do a great job of self-enertaining. Unless you call digging in the backyard, scratching at the door to come in, or barking all day at the neighbors a good use of their time. When dogs get bored they find things to do that we don't always find appropriate. A dog that spends a lot of time in the backyard without interaction also often shows up with other behavior problems due to the lack of overall time and attention.
One common surprise for new puppy owners is the rapid recovery time of a young dog. Even if you walk your dog at midnight instead of 10pm, there is a good chance he will be raring to go at 6am the next day (or earlier). Puppies have an amazing ability to recharge their batteries. Older dogs can take some time to get out of bed the next day, but usually not puppies.
Am I trying to scare you away from getting a dog? No, I just want you to realize one aspect of what is involved. I did not mention the financial commitment, grooming time, vet visits, what to do with a dog when you travel, during the day when you are at work, etc.
Shelters are filled with dogs left by people with the best intentions but did not think it through.
Stop and think it through.