Translation:What do you usually do in the evenings?
Is the plural "kvällarna" required here even with "brukar"? In English, the "usually" implies a habitual routine so "in the evening" is effectively understood as equivalent to "in the evenings": does Swedish work similarly or differently?
Swedish works similarly. You can say Vad brukar ni göra på kvällen and it would mean the same thing.
Thanks for the clarification. I have been wondering about this in other sentences. I always get them wrong because it is not natural to use the plural when referring to the date/time of a recurring action. Now the question is, are there exceptions?