I would second the vote for a UI change to a ‘calendar type.’
I have come to OpenSprinkler as a former user of Irritrol’s ‘PC Control’ system, which they have now discontinued.
While PC Control had it’s problems, what was really great about it and made it so easy to program was the UI for setting up and changing watering times. It was a 7 day graphical representation of the 24 hour day. You could see which zone was running at which time as a block of color on the calendar. The time blocks could be moved with the mouse, could be lengthened or shortened. Truly a great interface. (Unfortunately, the system in general was full of bugs, there was no support or corporate back up.)
If OpenSprinkler had anything similar I think it would be an amazing upgrade.