It happened three hours ago. Why haven't you contacted us before now?

Is 'before now' OK here?

anonymousIs 'before now' OK here?

Usually it's a bad idea, but people do say it, especially in circumstances like the one in your little scenario, when the implication is that something has been done too late.

But you would never say something like I've never been to Austin before now. You would certainly drop 'now' in that case. Or at least I would drop it.