Only one schedule may be set to end before sunrise. The other 3 options are start or end at a specific time, or to start at sunset. Over the course of the year the sun rises and sets at different times, so if you want to time it to a cool time of the day that varies by season, the only option for additional schedules, when the end before sunrise option has already been used, is to start at sunset.
The problem with this option is that watering will end at night, which increases the risk of fungal or other diseases form the grass staying wet for a long time.
I suggest adding an option to either end at sunset, and/or make it relative to sunset, for example plus or minus 3 hours from sunset in 30 minute increments. I assume after sunset times would not be used much, but perhaps they would in hot climates. In any case, if one set a schedule to start 2 hours before sunset, for example, the start time would automatically change as the time of sunset changes throughout the year.