I looked at the Star Cruiser voyage dates/the itinerary. Departure dates will be days that guests are either starting or ending their journey, and Batuu time is only scheduled for their full day on the ship. So for March, Batuu excursions will be on even days, in April and May, excursions will be on odd days, in June and July it will be on even days, then August odd days, ect. Guests get automatic fast passes to RotR and Smuggler's Run on those days, so there might be limited availability for lightning lanes. Savi's might have the opposite effect, where people go to HS the morning their journey begins to build a lightsaber to have aboard the ship, but they don't have priority for booking that.