I think what you are looking at is the watering duration for the instant manual run (not the user program) in the zone sections shown on the home page. The system remembers the last duration of the instant manual run and displays that on the home page.
The watering time for the program remains unchanged. You can go to settings->programs to verify.
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
Please let us know if you have any further questions.