Here's what I tell my clients - exercise has to fit into your life, or you won't do it. If an hour doesn't fit into your life, and a half hour does, and you will consistently go, then stop feeling guilty and do your half hour. And yes, I too would suggest you talk to the personal trainer, in order to get the most out of the time you do spend at the gym.
In addition, start changing the way you think about the rest of your life--get away from speed, move toward fitness. Instead of finding the closest parking space at the mall, take the furthest one away. If the office you work in is only two or four or five floors up, then take the stairs rather than the elevator. If the snatch-n-grab store where you get your coffee, newspaper or lottery tickets (whatever floats your boat

) is within walking distance, walk there and back instead of driving the car on Saturday morning.
Do you see what I mean? Take a look at your everyday life, and add walking, stairclimbing, and general effort into all the parts of the day that you can. Get a pedometer (they're like 8 or 10 bucks, tops). Set as a beginning minimum goal that you get to 10,000 steps a day. Each month, add another 500 steps to that. Check your pedometer just before dinner each evening--if you haven't quite made it, then go for a walk before or after dinner! Even if you take every one of these suggestions, you're adding at most a half hour of general exercise to your day, and you're keeping your metabolism burning throughout the day. Then you can use your targeted exercise at the gym to build muscle and/or get your heart rate up and keep it there in heart-healthy, fat-burning blocks of time.
Proud of you for going to the gym! And a point of advice--asking gym rats (yes, John and Gina, this means you!

) whether you're spending enough time at the gym is like asking a nudist whether you should wear clothes... LOL...