What about "Forgive me, I cannot stay for a long time." Can that be correct?
Should "Forgive me, I can not stay for very long" also be accepted here?
Yes, but it's still marked as wrong!
Forgive me...should be accepted for both. Same as Excuse me
Excuse me is "com licença" ou "me dê licença". It's like ask a permission for something. "Forgive me" is "me desculpa" or "me perdoa", which is the same thing that you apologize for something or feel sorry. Can you understand me?
Is this subjunctive? To me this seems like the imperative with identical conjunction to the subjunctive
No, it is not subjunctive.