Currently, the default manual duration when starting a zone from the RainMachine Mini-8 touch panel is 5 min (300 seconds). To change the manual watering duration on RainMachine Mini-8 through API use the Postman application.
Please follow this support article instructions and setup the Postman to use RainMachine API environment.
After you authenticate locally or remotely on the RainMachine Mini-8 using Postman interface go and:

• open the folder "Provision" 
• click on "POST  /provision"
• click on the "Body" tab
• and replace all code with the new one and the result will change the default 300 seconds (5 minutes) duration with 1800 seconds (30 minutes) duration. Change this amount of seconds to match your desired manual duration for each zone from 1 to 8:

  {
  "system": {
   "zoneDuration": [
   1800,
   1800,
   1800,
   1800,
   1800,
   1800,
   1800,
   1800
   ]
   }
  }

• click on "Send" command button to send the API call and save the new manual duration for RainMachine Mini-8 zones.

Note: If the Zone 1 on your RainMachine Mini-8 is used for Master Valve (Pump) this manual watering duration will be ignored since you cannot manually start the Master Valve.

Now every time you go and choose a zone to water from the RainMachine Mini-8 local touch interface the new default watering duration will run for that zone.

Thank you.
RainMachine Support