I answered from the word picker, not from typing, and got this:
You have a typo.
It is twelve o clock.
It underlined "o clock". Presumably it wants an apostrophe in the space there. But I picked the only "o" in the word picker, so there was no possibility of me getting this without the typo. It didn't have any option with an apostrophe for me to use.
Is this a bug in Duolingo, or is it a flaw in the data for this item?
I don't think that's the case, because it underlined "o clock" as the location of the typo. The word "now" would come before "twelve", in a different part of the sentence. Also, it would not be considered a typo because it is multiple characters - either the sentence without "now" is accepted as one of the correct answers, or it's not and it would be marked wrong.