The ET algorithm always uses yesterday’s weather parameters (temperature, humidity, precipitation), it does not include today’s precipitation so far, so the watering percentage calculated might not look ideal but keep in mind that today’s weather parameters will be accounted into tomorrow’s watering percentage.
Whether you use ET or zimmerman algorithm, it calculates watering percentage once per day, so the number remains the same until your local time crosses midnight. It always uses yesterday’s weather parameters — I agree that using the accumulated weather parameters over the gap between two runs would be better, but that would involve a lot more changes to the weather script, and it might not always be possible (for example, if you set a program to run every 14 days, I don’t think the weather provider gives history data of that long).