When you do it in spring, do it over two or three weeks rather than in an afternoon. Week one, an hour or two outside on good days. Week two, most of the day, still in at night. Week three, first nights out if the nights are consistently mild, with the shelter fully set up.
Slower again for young, old or delicate pigs. And watch the appetite and droppings the whole way through, because that is where it shows first.