Lunch duration should be at least 30 minutes (if you are law abiding citizens). In California, it's unpaid, but required. Your lunch duration should be based on a few factors that you may or may not consider, such as: proximity to food:. I there food in the office? What types of eateries are nearby? Is the office kitchen so small that usage of the microwave results in a queue? All of these factors matter a great deal. If you find that your team members need travel time to get food, at least 45 minutes is sufficient. With a 45 minute lunch, you'll just add 15 minutes to the work schedule.
You should also consider business hours. If you're office is open longer than 8 hours on any business day (and there is no work to perform after hours), hour lunches are certainly an option for you.
Here are examples of how schedules will work with an 8:00 AM start time:
[30 minute lunch] 8:00 AM - 4:30 PM
[45 minute lunch] 8:00 AM - 4:45 PM
[60 minute lunch] 8:00 AM - 5:00 PM