"Now we are a committee."
Translation:Nu er vi en komite.
Not sure how to explain it but if you split it up you may see why: Nu (tidsadverbum) er (abverbum) vi (Subject) en komite (object). I this case you have a inversion; meaning the verbum switches place with the subject.
It seems like it is usually with time expressions. Like Om mondagen er vi glade. Is this true?
Inversions are usual in "hovedsætninger" (main clauses?), in adverbiums and in "ledsætninger" (half-sentences?). If you didnt understand this, try looking at this page: http://www.danskherognu.dk/6/Grammatik-og-%C3%B8velser If you have any trouble understanding what is written, just let me know and I'll help you ;)
Does this mean that if we say 'vi er' with a time clause it becomes a question?
No, no. In a yes-or-no question you have to begin with the verb, just like in English. There's no space in front of the verb for any adverbials.