Elles (les chauve-souris) ne volent que la nuit

Bonjour Jennifer ! With moments of the day, you will usually use only the definite article "l'/le/la" to express a general statement: "Le soir, je me couche tard." (In the evening, I go to bed late.) "L'après-midi, il fait la sieste." (In the afternoon, he has a nap.) "La nuit, nous dormons." (At night, we sleep.) See also our lesson on days of the week: https://progress.lawlessfrench.com/revision/grammar/when-to-use-le-with-days-of-the-week-weekend I hope that's helpful! À bientôt !

Merci Aurélie, Prepositions one of my bêtes noires. I read your lessons but difficult to keep them in mind. Thank you again.

Courage Jennifer ! "C'est en forgeant que l'on devient forgeron !" (Literally: It's by forging that you become a blacksmith.) -> Practice makes perfect. :)