The Smartserver IoT Astronomical time function are computed for the location of the SmartServer using elevation angles for sunset and sunrise. Since there are no settings for elevation angles the SmartServer uses -6 deg for civil twilight.
This means that the calculated sunrise may be up to 44 minutes off. So for sunrise for some elevations SmartServer is 44 minutes early. You can compensate for this time offset in the schedule event using offset after of 44 minutes. The same is true for sunset, sunset may be up to 44 minutes late and so you may need to put an offset.
The amount of time you need to specify in the offset depends on the elevation of the SmartServer so the offset may be less than the 44 minutes.
There is a SmartServer Internal Device (AstroClock) that can be used to send sunrise and sunset times to external devices