[yorkieK9trainer]

"I would say two or three hours max. Keeping a dog in a box for much longer can lead to serious behavior problems."

Sorry, but I honestly have to disagree w/ you on that statement completely.
(one is to assume that you properly socialize and play w/ this dog also)

You can comfortably leave a grown dog in a crate for up to 8 hours w/o issues typically. Only in rare circumstances would it be advised against.
In an IDEAL world, you wouldn't have to. But it's not the end of the world and certainly won't cause any behavioral problems, quite the opposite, it prevents many from happening. MANY dogs-especially at a young age, regardless of the breed or sex cannot handle a larger area than what is provided in a crate. It's simply too much room and when the dog gets bored, rather than sleeping or chewing on the one or two items in his crate that have been provided, they tend to pace; bark; howl; soil the area; chew other things in the area that you initially didn't put in there; climb out; scratch at the floor and so on.

Crating is one of the more humane and safer ways to go when you're not avaiblable to that animal.
The longer you're not going to be around, the less water-if any-you should leave in the crate w/ the dog. This goes for food too. I personally advise against leaving food w/ the dog in the crate and often water all together. Feed him/her and potty them BEFORE they go on the crate for that day's work and then immediately potty and then feed/water when you get home.

Hope this helps!