Translation:Prynhawn Dydd Llun
Just now :)
Sometimes it springs things on you like that.
It especially likes to introduce synonyms or dialectal variants in multiple-choice questions.
So sometimes you'll just get a question wrong as there's no way for you to know, and then you look at the answer that was marked correct, perhaps ask in the sentence discussion, and learn it from there.
It's one way the course teaches you new things - by simply presenting them to you and telling you what it meant after you've tried to translate them.