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First off, great job! Working out really doesn't take that long. Most studies have shown that a typical non-steroid using weight training session only needs to last 45 minutes to an hour. After that time period, unless you consuming calories during the session the results you can get drop off dramatically from diminishing returns. I agree that the biggest hurdle with people going to a gym is the intimidation factor.…
"I want to tell them how awesome it is that they are doing it, but am never sure if that's the right thing to do some stranger lol." General heuristic: If you are not sure, if it is right to approach a stranger, just do it. Really. Talk to them next time. And don't end your sentences with "lol", please.
And in general your heuristic is correct, but the gym is an odd place. I'm pretty social, but would prefer no one talk to me while working out. I'm usually so busy watching the clock and focusing on the task at hand that I don't want to seem rude to someone by having to eventually ignore them to finish my workout.