I couldn't tell from your post if you are talking about a puppy or not, but it doesn't sound like a great idea for a pup. They will need to interact with you a lot more than an adult dog.
An older dog might adapt to that, I've always had a long commute to work, so am gone for about 11 hours. I have an indoor-outdoor situation for them; I have multiple dogs and they have access to a small yard inside our fenced property. They keep each other company. But they need some quality time from you every day. If you can't dedicate at least an hour every day to the dog, it might not be a good idea. At least a shih tzu at least isn't going to require hours of exercise, but it should get out for a good long walk with you every day, at least once a day. When I first get home I take them all out for a walk. If they get tired out, they are content to just be around me in the evening, lounging around. If I only had time to come home, walk them, then leave again, I probably wouldn't have dogs.
However, I've got one that is in kidney failure, so she takes extra time for SQ fluids in the evening, and feeding them all can take a while if I have to soak her food and hide all her medications in it.
If a puppy, or any dog for that matter, gets bored, they find ways to entertain themselves, and this means either becoming destructive or developing other bad habits. I think the idea of having two dogs is a good idea too, but you still have to give them lots of exercise and quality time with you, or you have two of them figuring out ways to entertain themselves with your stuff.
Even with an adult dog, the puppy pads are a good idea, and you'd need to spend a lot of extra time with the dog at first to gain it's confidence and develop a relationship. If it's an older dog, after that you and the dog should be able to get into a routine.
How much time each day do you think you'd have to spend with the dog? It sounds like you had a dog before, did that work out ok?
vickie