Butter metal 9-by-13-inch pan; arrange bread slightly overlapping.
Whisk eggs, milk, cream, syrup, vanilla, zest, cinnamon, and salt. Slowly pour over bread, briefly lifting slices to wet underneath.
Cover; refrigerate 8 to 12 hours, additional to listed prep and cook times. Turn unsoaked upper edges into custard once before bed.
Heat oven to 350°F. Foil-tent cold pan; bake 25 minutes.
Uncover; bake 20 to 25 minutes more until center 160°F and exposed bread golden. Rest 10 minutes before lifting portions.