An effective way of maximizing gym time and to get enough volume in to your training is to perform timed circuits. I quite like this approach as it not only burns calories at the rate of knots but also if specific you can see some strength gains carryover.
My approach this month is to use a work block of three exercises in this order- a push e.g. press ups, a pull e.g. pull ups and a leg exercise e.g. goblet squats. Repeat each of these exercises in sequence one after the other with 8 reps at a time for 8 minutes. Follow this with intervals such as short sprints or intervals on the rower and then pick a new set of exercises. About 3 blocks of work and intervals is enough for a workout and rounds out at an hour!