Hummelincki is diurnal but I found the Octane tended to nap (especially as he aged) and sleep (eyes closed and slowed respiration) in until about 2:00 PM then stay up until lights out at about 11:00 PM, basically adjusting to our schedule. All hummelicki owners have found them particularly human friendly. The only major down side is that they are a small egged species so tank raising is not currently viable. Octane actually initiated contact with us rather than the other way around. He required a very gentle touch (and I have since read that this is what others have found about O. vulgaris in the wild as well) and once he was confident with one form of contact would experiment with another. Eventually he would climb into my cupped hand in the water and use it like a tube to scoot through the other side. Octane was always very, very gentle and never suggested he wanted to bite. The closest to aggression of any kind would be to pull on my fingers if I had the smell of shrimp on them from feeding. However, every octo story is different and they each have distinct personalities so, by all means, try toys. Carol has had a lot of luck with la arge leggo block and Octane showed short interest in a leggo octopus with a long plastic tie hanging down so that it floated and had something to grab. We also played a little with a plastic ice cube and pushed it back and forth in the current. Octane (as well as two others I have noted) did not keep an interest in any of the toys though but another might.
You might look through the journals with the key word hummelincki to read some of the other interactions you might expect.