Ten minutes. Maybe 15 if I'm watching the telly at the same time.
I snip the strings at the tuner, like Sarah. It makes getting them off a lot quicker (esp. on the Lowden which has a pinless bridge, and the bit that's been round the tuner post doesn't want to go through the hole in the bridge).

"On another forum I've seen discussion about a winder attachment for an electric screwdriver. How many turns are these people putting on!"

If you were a luthier or repair-man, doing set-ups and other work on many instruments a day, you'd understand the benefit of that attachment!

For all the Johnny-Six-Thumbs guys out there:-

Here's a great resource