Translation:I will see you at the celebration tonight.
It's like saying "today at night". It's a common way to say tonight in greek along with απόψε.
''Σήμερα το βράδυ'' and ''απόψε το βράδυ'' are also correct alternatives. Εven though the second one may seem a bit redundant
True. Απόψε is tonight, so it's be like saying tonight at night. xP Σήμερα το βράδυ is pretty common as well, I'd suggest this one.
Απόψε is more correct. The only place you will see σήμερα τη νύχτα or σήμερα το βράδυ written and spoken is the weather report.
Yes, that is one reason we included it. There is a large vocabulary we need to teach and we have attempted to make reliable sentences.