You can start weight lifting, following a “Russian strength” program (just three exercises, heavier weight, small sets of 3-5 reps), and the experience noticeable changes within 4 weeks. And I’m not talking about a lot of time at the gym... perhaps 2-3 hours total of exercise per week.
Not only will you get strong, you will start burning more calories when you’re not even moving. Plus, you’ll feel more energy and more drive/discipline to eat better and go back to the gym. In fact, a common problem is wanting to go to the gym too often. (The older you get, the more recovery time needed between workouts... more workouts can actually be detrimental.).
And if you only have time to go to the gym once a week you can make visible progress in that much time. Three sets of five reps of squat, bench and deadlift is doable in 50 minutes and if you do it consistently once a week you’ll see steady progress for most of a year.