Shipped in 8.4. Pro users get a Start day at control at the top of the Meals screen. Pick a time — say 2 PM if you slept in — and every meal slides forward together. Breakfast becomes a 2 PM meal, lunch becomes a 6 PM meal, and so on.
Shifts apply today only. Tomorrow's reminders snap back to your default 9 AM (or whatever your plan's first meal time is) automatically — no need to undo.