Sunrise/sunset offset

Should be easy. I have a GE Enbrighten switch controlling outside lights. I want to create an automation turning the lights on 20 min after sunset and off 20 min before sunset. I can create the automation, but I just get one offset choice that works for sunrise AND sunset - nothing individually. Can I select the offsets I want in one automation or do I have to have one automation for sunset and another for sunrise?

You can use one routine, select period of time, night, sunset and add the time offset.
Then for the end time, select sunrise and adjust the offset time.

You can repeat everyday, or select days to run.

In your scenario, one Smart Lighting SmartApp Routine would do this, but not one Routine (aka Automation). Smart Lighting Routines are way more powerful with Sunrise/Sunset times than Routines (aka Automations) are.