If you say it happened three hours ago, why haven't you contacted us until/before now.
Does the sentence have the same meaning no matter which of "until" and "before" I choose?
Is one of them more natural than the other in a context like this?
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.Sign up to join this community
"...why haven't you contacted us before now" sounds more natural to my ear.
If you want to use "until," the following construction works better:
If you say it happened three hours ago, why have you waited until now to contact us?
The word "before" (in the sense of "earlier than" or "sooner than") works as a modifier to the word "now", while "until" indicates a time span ending at a certain point, which when used with the negative construction "why haven't you" tends to be confusing.