"I do not work Sundays."
Translation:Non lavoro di domenica.
Newb here, La domenica (Sunday as a thing; an object) and di domenica (of any Sunday) to imply all Sundays - it becomes plural one way or another. I believe this holds true when it is the subject, e.g. Lavoro di domenica (I work any sunday). Of course if you are speaking about periods in the past, the rules start changing. Using a as preposition (meaning to or at), you are speaking about a distance... in time - as per the category we're under ;)