Μία is in fact unnatural here. It would mean "does not have one belt", not "a belt". Here we only care about whether the person has (at least one) belt, not the number of belts that they have. the indefinite article in Greek is used when we actually care about the number, if the number can be greater than one.
This is wrong. I entered "she hasn't got belt" instead of "one belt" because there was no "a". It is very unnatural to keep saying "one" instead of "a", at least in English, and this course keeps suggesting that. Maybe in Greek there is no substantial difference between "a" and "one" because they are both μία, but there is difference in English.
What would normally happen:Αυτός would translate to this, and εκείνος would translate to that.
But: In English, it is now common to use that for things that are in short distance.
Long story short: Αυτός translates to both this and that, because this and that are interchangeable for things that are in short distance.
However, εκείνος is that, and that only. ^.^
[That] makes sense XD. But I think that maybe other mods have interpreted this a little bit different, since they have corrected other people when they tried to use [Αυτός] for [that] in other discussion threads (very old threads tough, so I don't know if they changed their minds).
You can't say "I haven't time for that", and you can indeed say "She does not have time for it", but time is considered to be uncountable. When someone refers to time as a concept in general, there's no such thing as one time, two times etc, only a lot of time, some time, no time etc.
Belt is a countable noun, so the article is necessary.