One work-around is to make use of the ‘watering percentage’ to help get the level of accuracy you need. For example, set the watering percentage to 10% gives you 6-second level granularity. Specifically, say you need to water for 1 minute 12 seconds. Because this is beyond 1 minute, the firmware doesn’t allow granularity to seconds. But you can set watering percentage to 10%, and set the water time to 12 minutes, then the actual water time becomes 12*60*10% = 72 seconds = 1 minute 12 seconds. (Forgot to mention: make sure you turn on the ‘Use Weather Adjustment’ flag of each program, otherwise the watering percentage will not be applied to the program).
Note that the water time itself is down to granularity of seconds, it’s just that the ‘stored’ water time has to be in granularity of minutes due to the limited storage on the microcontroller.
In addition, I want to point out that it’s difficult to design the firmware to meet everyone’s need. The reason the project is open-source is to give users the flexibility to change the firmware in any way you want. By adding a few lines of code, you can change the water time to fit your specific need.