I'm working on the Queen's Garb, and I estimate 3-4 days, depending on Giant Petal drops? I dunno. But since I only have 12 Cottages and struggled to spawn Grand Fire Fly, between 6 hour wait Giant Blooms and 4 hour wait Cottages, I'm working on Bulb Fruits and Fire Fly Fires in the meanwhile. So working on Goal 14 and Goal 15 at the same time. Magic Beans are last because it's only 10 minutes to grow. I'm using my Energy to collect all the Garden Elixir supplies first so I can craft the 2 hour items and not clog up the Potion shop at the last minute.
I can't confirm yet, but I think Goal 14's Queen's Garb will be the same as Goal 15's...