A literal translation would be ""How late is it?". This is an example, however, where we have the opportunity to learn how a German would naturally ask this question.
If we translated the English phrase "What time is it?" into something like Welche Uhrzeit ist es? we would be immediately recognised as foreign :)
I've definitely had cases where I've slept through the alarm clock and woken up saying "Oh, crap, how late is it?"
If Duo wants to teach us that this is the usual way to say "What time is it?" then having that as the default is fine, but certainly the more literal, also correct, and perfectly reasonable English should be, IMO, accepted.
... something like Welche Uhrzeit ist es? we would be immediately recognized as foreign
If I could offer a lingot with a smiley attached I would. That phrasing was essentially my first guess! However I think my accent will clue others in to this 'foreign person' pretty quick too.
It is a bit unfair to mark the correct translation as wrong because you are trying to teach people how Germans ask 'What time is it.' Why not just teach us that to ask the time you ask 'How late is it' instead of the stupid 'clever' way of getting people to translate a sentence knowing in advance that everybody will get it wrong. Why not just teach us the right way first time instead of all this stupidity and you only discover it if you then come into the discussion having got it 'wrong.' That is not teaching, that is being arrogant.
Anyway, in English it is perfectly legitimate to ask 'how late is it' if you want to know the time and it is late.
If we just assume you've asked that question, no matter how it would be phrased exactly, the answer would still be a time. So it boils down to the same question. I suppose you could say something like 'Es ist spät, aber wie spät genau?' if you absolutely want to emphasise that it is late already.
This has been brought up several times in this forum... I wish someone would give light to this question. I've tried placing it in google translate, but it literally translate "Wie viel uhr ist es" to "what is it o'clock". I know google translate isn't reliable, but just trying to get some clarity to this.
You'd specify what you were asking about, eg, "Wie spät ist mein Flugzeug?" Asking "Wie spät ist es?" refers to time, not to the time of a particular event, subject, object, etc. If asking about something specific, you need to mention that in your question, otherwise it sounds as though you're asking what time it is or how late it (the time) is. I hope that helps.
context is everything... if you were in a conversation with someone about your flight, so that it's clear that's what you're talking about (let's say they just said "your plane is going to be late") Couldn't you reasonably reply "how late is it?" And, how would you do that if "Wie Spät ist es" doesn't work? Would you still have to include "mein Flugzeug"?
"How late is it" is valid to say in English, and would be the more literal translation. It should also be accepted. Unfortunately there is a big discrepancy in that some exercises ask for literal and nonsensical (in English) translations whereas others expect a non-literal and don't accept literal.