They are two different tenses - your first is future continuous, and your second is simple future. The difference in meaning is slightly harder to explain, and depends quite a bit on the context of the phrase in the rest of the sentence. The important difference is that the continuous form stresses the continuity of the event. We are going to talk at 6. We are going to be talking between 6 and 7. We are going to talk tomorrow. We are going to be talking while you have dinner. Both '6-7' and 'dinner' take more than just an instant, and by using the continuous form, you are stressing that fact.

I think you accidentally repeated your question. I already answered the duplicate one.