1) you can use ‘seconds’ as watering period up to 59 seconds, then the granularity becomes minutes. This is mainly due to limited EEPROM storage. In future firmware we plan to make better use of the microSD card and thus eliminate this restriction.
2) The rain sensor circuit currently only allows the ‘stop watering’ logic, it does not have a ‘start watering’ logic, hence you can’t directly use it to achieve ‘start watering when sensor is activated’. This will require a firmware change to support such capability.