Here's a workaround (though not perfect) to allow one to add an offset to sunrise/sunset times. It's based on the fact that the earth rotates 360 degees in 24 hours, therefore one hour is equal to 15 degrees of longitude.
Normally Kasa gets its location info (latitude,longitude) from your mobile device, but you can set it manually. Go to Settings>Location and Time>Location and use the "enter location manually' link.
If you want the sunrise/sunset time to be earlier, increase the longitude (e.g., changing from -82.5 degrees to -75 degrees moves the sunset/sunrise time 30 minutes earlier). Don't change the latitude unless you want to get more or less hours of daylight than your default location.
Advantages: Fairly fine control over offset - just do the math.
Disadvantages: Both sunrise and sunset times are affected by the same amount. You can't change them in opposite directions. All devices are affected by the same amount of offset.
I agree that we need an offset for sunrise/sunset that will work on a per device level (for each schedule).