When my guy was eight weeks old, I set an alarm to let him out every two hours. I made sure I gave him no chance to whine.
If you can, try to let him out before he starts to whine. I'd say, every three or four hours. He will drive you mad at night if you let him think whining will get him out of the crate, and it will be difficult to stop this behavior.
Varick vom Haus Jeffery
Dark Sable, intact male
DDR/West German Show Lines