Another way of saying it would be: "What time are you open til?" (Spoken English, heard 44% of the time) "What time do you close?" (Written and spoken, heard 53% of the time) "Til what time are you open." (Most formal, heard 2% of the time) The remaining 1% of the time consists of mumblings you can't understand, by drunks asking when they can get their last beer.

It is much more common to say "What time do you close?"

More people would say, "How long are you open?" or "When do you close?"