Dumb jumpstart question: when to turn off donor car?

I've never jump started a car but need to.

Every guide and video I've found says to connect the cables, start the donor car, start the dead car, disconnect cables, and drive the undead car for a while.

None of the guides mention--When do I turn off the donor car? Do I leave it running while disconnecting cables? Or do I turn off the donor car before disconnecting cables? Or does it not matter?