I wrote "после шести часов вечера" and was marked incorrect -- is this a mistake?
No, you're absolutely right.
No, it's not technically wrong, the only thing is that the way you wrote it, it's like saying "6 o'clock PM" rather than just "6 PM".
It is too long. Correctly, in this case, "после шести". But it is my IMHO
Actually in russian talk everybody skip the word 'вечера' when it's clear a.m. or p.m. Here is dinner, so p.m.
I wrote "Я не буду ужинать после шести вечера больше." and otherwise from the grammar mistake, isn't it still technically correct?
You can say it with a stressed "не буду" as if you are making a promise. Otherwise it will sound strange.
Ну опять из-за того что слова не в том порядке пишет что не правильно
Could i use уже instead of больше here?
No, уже means "already"
It's the difference between saying "I already don't/won't do it" vs "I won't do it anymore"
"шести часов вечера" and "шести вечера" - are the same. Both can be used. "шести часов вечера" shouldn't be a mistake. Correct it, please
Is "Вечер" in the genitive case because it's seen as "Six of the afternoon"?
Nice, thank you!
Could it be стать instead of будет? I'm just saying, стать is on the notes but we hardly ever use it on the exercises, and it seems to me that it could be used here, as it could be a decision the person took.
Я больше не стану ужинать после 6 вечера. This is suitable too
IMO "вечера" can be dropped here
Can we say "поужинаю" with a future meaning (since поужинать is perfective), as an alternative to the "буду ужинать" form?