"Was he here at six?"
Translation:Byl tady v šest?
There is simply no reason, really. It actually is a lot of work to add unnecessary translations that someone might consdider "similar". It is not just "not accepting", it takes lots of manpower to add translations everywhere. To limit the necessary effort we have the Duolingo Golden rule.
But in other sentences, where hour is absent, answer without hodin is wrong. Such selectivity is wierd.