Could you say 我们上午八点吃早饭吗？or 我们早上八点吃早饭吗？to emphasize that it is in 8 in the morning and not 8 at night? I was marked wrong for those, maybe it is redundant to say 上午 or 早上 because you're also saying 早饭 ?
I understand what you're trying to say, but based on the sentence given no time period was asked for. So saying 上午/早上 for this sentence wouldnt be completely necessary. However when in conversation it can be used for your choice to distinguish the time period