Yeah, I am surprised that the hosts were surprised the OP was 5 minutes early. 20 minutes early is too early. But 5 minutes before a stated invitation time? If I were expecting someone at 6, I would kind of start expecting them about 10 to 6. Not "expecting" as in, wanting them to be there, but expecting as in, I'd better have clothes on because they could show up any time now or in the next half hour. If you don't actually want me there till 6:15, say 6:15.