If you want to run each zone for 20 min once per week with rain delay feature, you can try Netro's basic smart zone level. (Go to Settings->Zones->Smart Zone)
In this level, no smart schedule will be generated. You will need to add programs manually (go to Settings->Programs to add programs) and Netro will skip programs when there is large amount of rain(>0.2inch/ 5.08 mm) or watering regulations.
For more information about Netro smart watering, here is an article about Netro three watering modes which might be helpful. https://netrohome.com/forum/posts/111