One reason a lot of us have a hard time getting to the gym is because we don't have the extra time it takes to complete a workout. This could also be the reason a lot of us skip cardio or strength training completely.
Instead of cutting yourself short, cut your time down. A simple way to cut out a few minutes at the gym is to shorten your rest time between sets. I am not saying don't rest, because your muscles do need some rest time. However, instead of taking a 30-60 second rest in between upper body sets, work in lower body sets. For example, do 12 hammer-curls then 12 lunges then rest. Now repeat two more times. This way, the muscles you're working are still getting a rest, but you're still getting on with your workout.