I wrote this solution for those gamers who cannot unlock this achievement, because the app always crash. My app closed every time after 3-4 hours, but I succesfully did it in this way on first try.
The first thing you must know, you can watch past broadcasts
too, not only online live broadcasts. Now you have to find an 8-9 hours or longer video on Twitch. The best channels for this are Twitch and TwitchPlaysPokemon, because they have the longest videos.
Now check your network connection and console. I prefer to use ethernet cable, but may a WiFi connection works too. I used 100Mbit wired connection with 10/1Mbit internet connection. Disconnect all wired and WiFi internet enabled devices in the house, phone, tablet, TV, other console, media server etc. Close every application on your Xbox One.
Launch the Twitch app and snap the Achievements, so you can check your progress. Set the video guality to Auto. If your picture is not clear, have a lot of pixels, you must restart your modem or you still have some device on your WiFi network Start a long past broadcast and turn off your TV.
After 8 hours the achievement should unlock.