Sometimes 1 second, sometimes 5... Or whatever level you have worked up to.
Practice this exercise for no more than 5 minutes at a time, but practice many times a day, if possible. Stay right with them until they are calm and quiet in the crate with the door closed for 5 minutes.
Then proceed to move away from the crate. However, you have to go back to having the door closed for a very short time. So close the door, take one step away, step back and open the door before they cry. Keep working up to moving 5 feet away from the crate for 5 minutes in small increments as outlined above. Be variable. Don't respond to crying. If they cry out, just hold still without looking at them or talking.
If you find that they are getting louder and more stressed sounding with their crying, or you think they may need to go outside, make a sudden noise in another room... like closing a door or dropping a book... just enough to make them hold their breath and listen for a moment. In that pause, start talking to them and get to them as quickly as possible. Take them out, change something in the "picture" and regroup. *Do Not* go to them and talk to them or look at them when they are crying (and I know they can really scream at times) or you will undermine all the work you are putting into teaching them to be alone and quiet. Since you have rewarded them (by going to them) after 2 hours of crying, it is likely that they may try crying that long (or longer) again. If you follow the steps
I've outlined above, hopefully you can bypass the stress (on all of you) of all that crying. If you give in and go to them when they are crying you will be teaching them that crying "works".