If you use the official features, it’s easy, but you have to have two different automations. One that occurs after sunset and one that occurs before sunset.
Alternatively, you can use core, but setup for that can be quite complicated, so it might be overkill for this situation.
Yonomi does not work with SmartThings at the present time. There are some community members who use it, particularly for management of harmony or Sonos, but not for your basic smartthings – controlled devices. But as far as those go, core can do everything yonomi can and more.
