I don’t think there’s a setting like that. Assuming your lawn is not being watered every allowed day, perhaps increase your crop coefficient under advanced zone settings. Adding 10% may be a good start. This means you’re telling the controller the grass is evapotranspiring/ using more water, thus increasing water frequency (not duration). Take a look at the soil moisture chart when you’ve adjusted that and see if it is watering more to your liking. Or if your lawn is already being watered nearly every allowed day, the other adjustment is increasing advanced zone setting’s root depth by an inch or two. That’ll easily increase water duration. Again, look at soil moisture chart to see how that affects watering. Or try both settings. You can also manually change water duration under schedule if you’d rather not touch your settings. That’s totally legit but will be overwritten if any zone settings are changed in the future.