"When will they be ready" should be accepted
Complete agreement with the comments below. "When will they be ready" is a much more natural expression.
This is not a sentence that would be said in Australian English. When will they be ready is better.
Same in the US
when will they be ready. did not pass
"when are they ready" doesn't seem like something anyone would say. It would be either "were ready" or "will be ready".
This gentleman in unintelligible! Has a very bad pronunciation !!