The biggest factor that determines whether the balcony is in shade is the superstructure of the ship, if the sun is on the other side of the ship to you, then all balconies on your side of the ship will be in shade regardless of the time of day and the sea walk will make no difference. If the sun is on your side of the ship, in March the sun won’t be very high in the sky (although it’ll get higher in the sky the further south you go) and again the sea walk probably won’t make much difference.