"The festival runs until Sunday night."
Translation:O festival vai até domingo à noite.
I wrote "o festival vai até domingo de noite" but the answer was "o festival vai até domingo à noite", so which one of us was wrong or were we both right? :D (me and the program)
In conversation we someties would say "de noite", but that would be linked to the expression "at night". If we say "monday(days os the week)/tomorrow/yesterday", we use à noite.
Yup, specially if it is a special single night. We use them in the past. "A noite de domingo foi ótima"