The firmware actually already rejects water time that’s too short:
https://github.com/OpenSprinkler/OpenSprinkler-Firmware/blob/master/main.cpp#L734
specifically it won’t water if the watering percentage is less than 20% AND the water time ends up being less than 10 seconds. The logic of the first condition is that if the watering percentage is high, that indicates the user intentionally wants to water a short duration.
Of course this can be easily made into editable options: like if you want the threshold to be 20 seconds instead of 10 that can be easily changed. We can add this as an option. In the mean time, if you are interested in giving it a try, you can modify that line of code and recompile the firmware yourself.