All right, it seems like we've agreed on 6 PM or around there, so I went ahead and signed us up for that. ^^ I'm not familiar with Kumoricon, but at Sakura-Con, the karaoke auditions were in the evening on the first and second days, so I was worried at first. But it sounds like the auditions are earlier at Kumoricon, so we should be good.
Which cosplay I wear will most likely depend on the temperature. If it's not extremely hot, I'll most likely attend in my Luka's-red-kimono costume, since it's comfortable and fun. Though I do have a normal Luka cosplay as a backup, which doesn't get hot as fast.