For my current job I asked during the interview what a typical workweek was like here. They said 40 hours, with an occasional extra 5-10 a week, and a very rare extra 20 if it's a big project that has something weird happen. I was up front with them and said I don't mind working extra here and there as needed (and mentioned times I'd done it at my last job), but I don't really want to go somewhere that my workweek is going to creep up over time to being 50-60 hours standard.
If the company is smart, they won't hire you if you make it clear at the beginning that you don't want that kind of job. This place hired me and I'd say there's maybe 2 weeks a year I work over 40 hours.
With that being said, plenty of people here do put in 50-60-80 hours a week, and I'm sure they complain to their friends/family about how rough the company is on them. I know plenty of people like this who impose these crazy schedules on themselves and assume they'll get fired if they don't do it. If you only want to work 40 hours, just work 40 and see what happens. Maybe do an extra hour here and there for projects you know are a huge deal. Until a superior at work has explicitly told you you aren't working enough, I don't think you should worry about it. If a superior does approach you about not working enough, just be genuinely curious about what the expectations are, and mention your interview process and how it went. Again, reiterate that doing it once in awhile is okay, but ask if you're really expected to be checking your email at 1am every night. If you are, or you can tell the person is pissed, start looking for a new job.
The reality is, even companies that only require 40 hours aren't going to stop you from pushing yourself to 50-60+. That guy in Hong Kong isn't going to tell you not to respond to him, because there's no downside to him. There will always be more work, if you take it all personally you'll work yourself to death. As far as I'm concerned if your 40 hours isn't enough to get all of your work done they need to pay you more for extra hours, hire more people, or accept that things will take longer. I literally have enough work to last me for the next 2-3 years if we stopped taking on new projects today, and I still work 40 hours a week. The work will be there tomorrow when you get back, and the more you do the more they'll give you. You have to take some initiative and actually talk to some people rather than making assumptions. You could also have a conversation with your boss about these concerns, depending on how comfortable you are with him.