To be exact...
It takes several revolutions of the wheels for the hubs to actually engage after pushing the button. Which is why it would be bad to be in 4x2 mode, get stuck, push the button, and floor it. Baaaaaad, but I can confess to making this mistake before.
For the hubs to disengage, the transfer case must be in 4x2 mode, and the front wheels must rotate in the opposite direction. So if you were in reverse with 4x4, you would push the button again, and drive forward a few feet. Confused yet?
And, when in 4x4, don't change directions and floor it quick, because when you start going the opposite way, the hubs will disengage and then re-engage.
I've worked with them before. Let me or us know if you have any questions about them, including preventive maintenence (very important but not hard) unless you've read already.