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.
:)