Samsung runs an interesting site in Turkey, the name of which translates to Are we up to date? and it does what it says on the tin. It tells you the planned release date of upcoming Android updates for the companys Galaxy phones.
Obviously, this is for Turkey and schedules can differ from country to country but usually not by much. Heres the Android 8.0 Oreo schedule for some of the more interesting phones:
The Galaxy S8 duo is already on Oreo (here’s the changelog), though the rollout didn’t exactly go smoothly.
Source (in Turkish)