For openers, you can split body parts. Working the legs and arms one day, then working the chest and back one day, then working the shoulders and abdominals the next day is a good, effective way to shorten your exercise time and still give each muscle group a good, solid workout.
Another thing you can do is keep it down to one set. It is usually not recommended to do only one set during exercise despite claims made by other experts that one set can be as beneficial as 2 to 4 sets. But one set, as long as it is one good set, is better than doing nothing at all if time is the issue.
You can also do a circuit style workout with your weight training. All you do here is complete one set of one exercise, then move right along to the next exercise non stop until you've finished each exercise in your routine. Once done, you take a 1 to 1 1/2 minute rest period for some water, and then start on set two until you've finished all of your sets.
If you haven't done it before, a superset style workout can save a lot of time. This is where you work one muscle, and then work the opposing muscle or you do two exercises for the same muscle without a break. An example would be doing a bicep exercise followed by a triceps exercise. Another would be doing bench press followed by chest flies.
You will need to have a workout plan. A lot of people in the gym wander around looking lost like they are trying to figure out what to do next. That is one of the biggest time wasters there is. Have an exercise routine planned and written out on a log so you know exactly what exercises to do and in what order to do them.
Probably the one single thing that wastes more time in the gym above all is socializing. Either reduce or completely cut out "chewing the fat". You may know people in the gym and they may have the time to approach you during a workout for conversation. If they do, just keep moving along while they talk or explain that you are on a time crunch and don't have the time to talk right now. They usually will understand and leave you alone.
More often than not, you can save quite a bit of time by keeping these things in mind and remember to just keep moving. You get more from your exercise program by spending 40 minutes in the gym with 30 minutes exercising than you do by spending 90 minutes in the gym with 30 minutes exercising.
