Scheduled to Week (Week -of May-14-2018)
That puts shipping at 4 weeks from production to delivery, which seems about right (especially since the Flat Rock plant is notorious for shipping delays), and about 14 order to production, which seems a bit long but also makes sense. The Flat Rock plant doesn't produce cars as quickly as say Dearborn Truck or Michigan Assembly so that could lead to some longer wait times. For what it's worth, the latest fleet bulletin shows a lead time for Mustang at 10-12 weeks and I know they've been working overtime lately so there's a slight chance yours could be built a few days early.
Check back in a few weeks before the week of May 14 and you should have a more specific build date.