No, that shouldn't be necessary. This is a 'mix and make' recipe and you can fry the fritters immediately after they have been mixed. If you would like to mix the fritters ahead of time you can store the batter in a covered container in the refrigerator for 24 to 36 hours. Give it a quick mix before frying the fritters in case the grated courgettes have drawn water. If this has happened, stir in a small amount of flour before frying.