It's "är det" instead of "det är" because it's preceded by "Nu." Am I correct?
The word order there doesn't sound very natural. The other order I'd agree with is: "It is too late now"
I don't think it is too unnatural, like ''Is it now too late to book a room?'' sounds fairly natural to me.
Ashley, I find "It is now too late" equally acceptable, though it is perhaps not the most common usage these days; it might sound a little more British, in fact. I can imagine myself (and have probably said) "It is now too late to catch the 12:03 train" and so on. [I'm a 60-something American writer, and have lived abroad--Britain (10), Asia (5) and Sweden (2) for the past seventeen years.]
Again, I guess this is the adjective instead of the adverb form in this sentence?