How does Allrad work in the new transit?

Good evening, I have read that the all-wheeled transit normally drives with rear drive and the front wheels switch on if necessary. Does anyone know something more precise? With what response time the front wheels turn on? React immediately when the rear wheels turn on or you have to stop and start again or you have to turn on while the front wheels turn on, etc. Has someone already learned something about it. I am very curious how this will work….