I believe those two can be trained to be diurnal or crepuscular (feed at twilight). I could be wrong, I am by no means an expert. I would suggest adamantly reading the forums for information, there's tons of good info!
From what I've read they can be 3" mantle with 18" tentacles, sometimes bigger or smaller. I've seen that 55g is the suggested minimum tank size for either of those species.