I haven't worked in a Japanese company, but for 6 months last year I worked with a Japanese company and their engineers. I'm a mechanical enginer and my company builds tooling and automation equipment. I worked with their mechanical and manufacturing engineers.
In general their work habits aren't any different than US engineers. If you have something that you need to do you work as long as you have to. If you don't you go home at 5 or 6.
During an early design review we were a little behind in the agenda but we left at 6 because there was enough time the next day to cover everything. We actually finished that next day a little early.
At several later design/schedule meetings and during the install process they were generally at work until 8pm or later. In this regard I didn't see any difference between US and Japanese engineers.
The largest difference I saw was in the very regimented seniority and the way it was expressed. Their head engineer would occasionally ask one of us for some information. When we gathered that information we couldn't go back to him, we had to talk one of the younger engineers and they would relay the information. Additionally, senior engineers would often ask younger engineers to deal with menial or secretarial tasks.
And because this is the first company you will work for, it doesn't matter what their culture is, you will consider it normal.
It is that way for me where I work.