Young puppies who can't control their bladders shouldn't be left alone for long, but most trained, well behaved dogs should be fine an entire work day. Scout's had an occasional 12 hour day, but for the most part 4-6 hours, although he could care less if I'm home during the day. Keesha had days up to 14 hours without accidents, but she had separation anxiety for years, so there were other issues, regardless of how long she was alone.