When I use to go I would do the treadmill for no more than 30 minutes but that was when I didn’t have the energy to get my heart rate at a good level. For me getting it between 140 and 160. The higher the number the less time I spent. So I could only maintain at 155 for 20 without getting winded. If I was at about 140 I could last for at least an hour but I always felt a half hour was more than enough to hog a machine.
I found though the eliptical bike gave me a way better workout without hurting joints. Running on a treadmill would always cause me knee or ankle or foot injuries. Elipticals were way better to my joints and feet and I felt gave me a way better whole body workout. It would firm up all the places I needed to firm up and helps even out your core. It engages all of your muscles. Legs, butt, arms, chest, and even stomach if you do it right, and waist. Kills a lot more calories as well.
Once you get use to it, it gets easier. Start with about a goal of 10 minutes and then move up to 15, then 20. Once you are on twenty, move it up in difficulty slowly every 10 minutes. Then once you get it to a difficult level. Go up and down. 2 minutes hard, then 3 easy then 2 minutes hard and 3 easy. Then once it all becomes easy again, go up higher. The idea is to always challenge yourself . You burn more calories and get a better burn going in cycles.
Be sure to drink lots of water. People don’t need more than 45 minutes at a gym.
There were other things I use to do but I honestly don’t remember all the names of them. I would call one my stomach bench and the other my leg weight machine.