There's a common misconception that the longer you spend in the gym the better. This couldn't be further from the truth. What you do in the gym is far more important than how long you spend there.
That's where full body conditioning comes in. Short, sharp and high intensity is the best 'bang for your buck' method for losing weight quickly, alongside a good nutritional program.
My go-to for full body conditioning is to super set an upper body exercise with a lower body exercise. A super set is two exercises performed back to back with no rest in between. For example, squats and press ups.
How to structure it? Set up a timer for 60 seconds and do as many repetitions as possible in the time frame and move straight into the second exercise at the end of the 60 seconds. Give yourself 20-30 seconds rest after each working set and repeat 3-4 times.