So spend half an hour exercising every day. It's still a lot more than nothing and well worth it when "family time" involves saving someone from a burning building or some other sort of emergency and you have the physical strength to actually do it.

So don't spend two hours. Exercise isn't an all or nothing game. There's a TED talk out there somewhere (google it) which explains that you get exponentially more out of exercise from about the 15 minute mark, and it hits a peak around half an hour. The study showed that the single best thing you can do for your health (the closest thing there is to a silver bullet, if you will); and this applied to both average sized people and the obese, smokers and non-smokers, etc, was to get 30 mins daily exercise. But even if you can't get that much, 15 minutes isn't wasting your time.

Furthermore, exercise doesn't take up your time, it actually increases it. Not just in the years in your life and how much less time you spend in those years being sick; that's obvious. But every single day.

Tim Ferriss tells this story about how Richard Branson was once asked the single biggest thing most people could do to increase productivity. Due to the fact that he's one of the busiest men on the planet, every single person in the audience leaned forward with bated breath. His answer? Exercise daily. It improves the quality of your sleep, so you need less. It makes you more emotionally stable, so you're more motivated. And most importantly, it increases mental clarity, so you're more focused through-out the day. Branson said that it gives him multiple hours more productivity every day. It's bull to say you don't have enough time every day to exercise; if you're that busy then in fact you don't have enough time to NOT exercise.

Finally, just thought it was worth mentioning that half hour of exercise doesn't even have to be strenuous. In the study I mentioned before they recommended walking, because it's the best overall for your body (too many people run on concrete these days). Swimming is also very good. Neither of these have to be exhausting. Hence why I take the 30-35 minute walk to work every day. My other exercise is a bonus.

I do convict conditioning for 4 months now. It takes me approx. 30 min every other day although I switched to more like 20min 6 times a week now. The results are spectacular. The important thing in exercising is not to overresearch, eg. you can find all kinds of people on the internets telling you that convict conditioning sucks and you should rather do X. Lots of these people have a point but usually it only holds under specific conditions like "I want to maximize my expected strength gain." but ignores time, financial or risk adversity to injury. TLDR: Just pick something that fits your constraints and stick with it. The results compared to doing nothing will blow you away.

All the literature I've read for bodybuilding says your reps should be in the 8 to 12 range, and higher reps leads to more muscle endurance without much muscle growth.