Exactly that. It's possible, I imagine, that he did more than this. But from sources, that is the *only* thing we know for sure he did. I'm not sure where the thing about the tickets came from--other than Mikio was very much into theatre and it seems very likely his local group was bookmarked in his tabs. Moreover, we know he had been involved in theatre stage SFX and design, so on. He was also an illustrator / artist (the thrust of his work at Interbrand, as I understand), and worked on the Inspector Gadget anime. So, all that to say, it wouldn't shock me if he had a theatre group on his favourites and the killer clicked on it. But how intentional that was, whether or not he actually had a common interest, or perhaps he simply clicked on the first tab he saw to play around with Mikio's credit card details on some such, we simply don't know. At any rate, this is all speculation. As you say, only the creation of a new folder is confirmed (on the desktop, I believe).
I'm not sure he called it anything. Or even if he intended to do that. Even accounting for boot-up time (assuming the computer was off, I think it was ON given Mikio's actions just prior to the murders), five minutes seems like a long time to just create one folder and do nothing else.
All possible, we simply don't know. An interest in gaming wouldn't shock me at all. And yes, he was on for exactly five minutes. (He also did NOT pull out the plug as some have suggested on Reddit etc). If I had to guess, the killer is at least proficient in Japanese given he seems to be going through the family's documents, using a Japanese keyboard, so on.