It really depends what do you want to achieve.
As a regular guy, if you want to gain muscles and strenght 45 mins is good enough. You can have really good gains with just 45 minutes per day, 3-4 times per week. 5x5 system is quite good (squats, deadlift, bench press or overhead). You can add biceps (pull ups, curls, ...) and rows. 5x5 will do it in just 45 mins. You will most likely qain weight once you start lifting heavier weights as your body is producing anabolic steroids that build muscles. Your bones will get stronger (and heavier) as they will deposit more calcium.
If you want to win some bodybuilding competitionm well 45 minutes 3x per week won't do it, you will be a joke. You probably want to add to it at least 2 more days, and probably extra time for other body parts and extra excercises. You will probably gain lots of weight but this is weight due to muscles (of course if you are careful with what you eat).
If you want to deadlift 1000 pounds or 600 pound bench press... Well, see e.g. Andy Bolton, if I remember he excercises dead lift only 1x per week. That is right, the rest of the week he rests (and of course excercises other parts of the body). You will gain good muscle mass, but you will also gain good amount of fat. And of course, as a powerlifter you will gain lots of strenght.
If you want to lose some weight you probably want to work out more than one hour, especially cardio is good, some combination of running/walking, swimming, biking... You are burning fat but also muscles. Have you ever seen fat long distance runners? I don't think so. Once you do "longer" distances and "longer" time, your body switches to cortisol, which basically breaks down muscle tissue and fat, and also makes your bones brittle as it removes calcium. Do 5 miles per day, 2-3 times per week. The other days try at least 50-70%. You will comfortably lose lots of weight, you will be light and skinny. But you will also be weaker and your bones will become brittle.
If you want to look muscular without lifting too much weights try sprinting short distances, run as fast as you can with breaks in between. Run up to the hill. Avoid running long distances. You will be skinny and muscular, assuming that you are on good diet.
You can of course use any combination above, depending on what you want to achieve. For regular guy you don't have to go crazy. Lift some weights 3x per week, 45 minutes is good enough (try 5x5 as above with range 200-300 pounds, you will get excellent results). You won't become a pro, but will gain lots of strenght and quite good muscle mass while spending minimum time in fitness. The other 2-3 days you can do some running, sprinting or perhaps just jogging, 2 to 5 miles per day (e.g. if you need to keep lean). Eat quality meals. After couple of months you will be in great shape.
DIET: It also depends on what you want to achieve. For gaining muscles you probably want to eat more protein. There are also different kinds of diets, but in essence you want to have some sort of balanced diet where you are not avoiding proteins, fats or carbohydrates. All are important, and avoiding any of these is not healthy and it doesn't work anyway.