We plan to add an option in the firmware to smooth out the watering percentage (basically keeping track of the call results of the previous day and take the average of all of them). This will make sure it gives a single number per day.
At the moment if you notice significant fluctuation in the watering percentage (like more than 30% in the morning vs. evening) that’s likely due to predicted rain — as I said, the rain prediction by OWM can be quite unreliable so that can result in large changes. One solution is to suitably reduce the weight of ‘rain’ which you can adjust in the weather options.
Temperature and humidity is unlikely to result in significant fluctuations because the rolling window is already taking the average of temp/humidity of the next 24 hours. Even if they vary across a day, the average over the next 24 hours usually does not change very much. So as I said, any large variations is likely caused by incorrect rain prediction.
You can submit a support ticket with your specific location, and we have a script to track the watering percentage for your location for a couple of days, which can show where the fluctuation is coming from.