I personally wouldnt leave my dogs any longer than 4/5 hours.
I think each dog is different and you get to know how long they do and dont mind being left.
I dont think its fair that I leave them longer than 4/5 hours and I rarely do it.
Then again I work from home so I have an advantage.
If I have puppies I dont go out at all!

Dont think there is a single answer for this one.
