For now I would set the front yard to a fixed spay head setting to match the rest of your zones. This is the reason why it was giving you a different time for that zone.
Here is more info (link) on the differences between spray heads.
If you notice that your front yard is suffering prom being under watered, you can adjust the settings to increase the watering time (that is a topic for another time).
Meanwhile, considering that you have only three zones, you can upgrade your valves from parts available at your local store (like home depot), it is a worthwhile DIY project. Here are some examples: (link), (link).