Gouldian Moult: How Long?

My adult Goulds are starting their yearly moult (getting bald spots, losing flight feathers), and my youngsters (14 weeks) have started getting dots of color here and there. I’m in my first year of keeping birds, so this is my first moulting season.

Question is: How long should this take? Also, is there anything special I should be feeding them now? They’re still getting germinated seed and egg food most days, plus greens, eggshells, and spray millet, in addition to their seed mix. They get iodine and calcium supplements, plus multivitamin drops in their water.